From what little I've gathered, Square is one of the few major Japanese gaming companies to which there are no issues with Japan's foreign investment rules. The other being Capcom. As I understand it, that is because they are the only two who did not have ventures that fell into protected categories when Japan got really defensive of their economy during COVID. So while there are other potential issues in trying to buy them, there does not appear to be a government issue.
Square has now done two successful MMORPGs. Some would argue those are what helped spread the concept of GaaS.
Square also has a pretty strong mobile presence. Something Sony wants too. Also, Sony, not too long ago, said they were going to make strategic investments, with an emphasis on IP.
They want those transmedia opportunities and Square has a fair few to pull from.
In addition to it almost certainly being a defensive move if they do it, there are other good reasons why Sony would want to own them.