Prototyping, hiring staff, growing their tools and pipelines, etc? Games at that scope take a long time to make especially brand new studios.
Preparing something for E3 has to be fine tuned and polished. It takes months away from ACTUAL production work because the vertical slice, demo, whatever, is often a WIP that will change quite a bit when it comes to actual shipping. This mattered more when demos were made for E3 instead of just trailers now, though. If they decide to make something for E3 that's great, but it's likely they've only been out of pre production for maybe over a year. Factor in covid and you don't have a lot to work with.