For one thing, its absolutely in the interest of anyone supplying product to an online storefront like Steam to ensure that their rights are being protected. Because if they aren't why should they expose themselves to the risk? Most suppliers don't offer DRM-free product for this reason, and what's worse this would legal. They'd literally be cutting their own throats for no good reason. At the very least they'd be better off selling their product directly as the presence of a middleman like Steam suddenly loses most of its value to them.
Sure, but it's their choice to do so. As i said before, nobody forces them to do so if the benefits aren't good enough for the costs. DRM-free storefronts exist too, after all.
Besides, digital storefronts would still give an increased visibility to the products, and buying from it would still be considered more secure than doing it from some half-baked website of some unknown developer. As far as big companies go, then sure, they may think it can be more profitable selling their products directly...and as a matter of fact, that's why we've got a ton of them making their stores/launchers so that they can do it as well.
Suddenly the prospect of not actually selling directly, but instead offering solely through streaming services and other "rental" type arrangements becomes MUCH more appealing.
Good luck making streaming services work all over the world. Besides, any other arrangement would still come under scrutiny of the law.
As to "trusting the consumer", well, there are two major drawbacks.
First of all, its not just about the customer. Its about suppliers protecting themselves from other businesses that would exploit customer freedoms to enrich themselves at their expense. I'm talking about services that harvest large numbers of "used" keys and codes, often from dubious sources, and then sell them on for a profit. This is the major point that most people seem to miss when talking about the negatives of DRM and copy-protection, its not just about the consumer, its about defending against large-scale enterprises exploiting the situation. Entities that add nothing to the scene, but simply see it as an opportunity to make money.
As long as they come from legally clean sources, so be it. Customers would profit more from selling their keys/codes directly, but if they want to use a middleman or sell those keys/codes for peanuts...well, it's their loss. Not so different from how it used to work so far for used physical games, anyway.
Secondly, it massively encourages digital theft. Suddenly getting access to somebody's Steam account is a potential windfall. Deactivate, sell-on, delete the account. Boom. How are you going to prove that this wasn't you? You expect Steam to chase up the reseller and find out to whom the funds were sent (good luck getting them to turn over this info without a court order) in order to validate that it wasn't fraud? Nope. Its gone.
And that would happen because we don't have a proper legislation about property of digital goods. And we don't have it because companies did whatever they want and most customers were - and still are - fine with it.
There's a bunch of other stuff to be considered too. Why offer trial periods allowing refunding when the product can be sold on at will?
Because, as far as Europe goes at least, we have customers rights.
In normal circumstances, as a customer you can also examine the product and refund it back, as long as you don't use it. That happens because using it would cause a depreciation, so it would incur in a compensation.
But as many people already said, there is no different between an used software and a new one, so there would be no reason for a depreciation either. Seeing as the only way to see if a software works is, well, using it, it's not like there is any other way for it to work.
Steam refunds work like they do because if they weren't "customer-friendly" enough to make things good for both customers and themselves, someone would already have gone straight to the court to make them fix it.
I'd question the assumption also that this would have no effect on pricing, as effectively this will require additional investment to setup, and spending to handle the potentially large numbers of digital transactions, complaint handling, and general servicing required.
Again though, I keep coming back to the thought that the crux of the matter is that unlike selling on something you've bought physically, digital resales require the product to be manipulated by an outside party in order to be sold on. That in itself is a service, and services are never unconditional and always cost money for somebody. Expecting a free, no-strings-attached solution is to my mind, extremely improbable.
You're conflating the issues. As far as customers go, to sell a DRM-free game a private transaction and transferring the data would be enough. No outside party involved. But it works because the concept of property of digital goods is a grey area.
The issue you have is not about selling digital goods.
Your issue is that you want for companies and storefronts to still have control over something they've sold, well after they've sold it.
Well, they're not the police or something, so why should they be able to? Because it worked like that until now? Eh, things may change once a proper legislation gets done.
With physical items, it works with a proof of ownership (the receipt) and the item itself. With digital items being considered resellable there may be changes - but there can be only if proper legislation gets done. And sure, it will likely end up requiring an outside party, but it wouldn't end up being the companies themselves, but rather something appointed by a state, or some supranational entity. As companies have no say upon the property of something they've sold. But states do (and a supranational entity would work better, in that regard, so that the legislation is already unified from the start).
Its a Pandora's box of horrors frankly.
I agree that it will cause issues. But it couldn't be otherwise - it should have been done far before. Companies spent tens of years profiting from a nebulous legislation, cherrypicking only what was deemed profitable from those laws. Once a proper legislation is done, it is no surprise that it may end up less profitable for the single actors (not necessarily for the whole market, though). Either we open that box now, or we keep piling issues in it and wait for it to explode.