I know several top managers who are in favor of mandatory RTO for those lower ranked than themselves.

Not all of the stakeholder's voices are in the room, right? Something that's essential for Big Tech is the wave of newly minted engineers to facilitate growth (and replace people that retire). These people don't even work for your company yet, but I know that the're going to have an awful onboarding experience when there is nobody to sit next to them and answer all the "dumb questions" that we inevitably have when we're learning the field.

My impression from working at Google was that mentorship was one of the most important software engineering job responsibilities. There were many summers there where I had interns and my full-time job was answering their questions, and that seemed to be what was expected. (They made some neat stuff that I would have prioritized for myself to do!) Big Tech's goal is to get huge, so they can pursue any opportunity that comes up. It isn't necessarily for Engineer #23847 on Team #8734 to type in as much code as possible.

(Whether or not this strategy is a good idea is up for debate, several rounds of layoffs later.)

Same here. And it makes perfect sense.

For me personally, being able to move somewhere with a lower cost of living without having a lengthy commute is a huge benefit. Especially in the face of ongoing layoffs.

That's hardly a qualifier, because I work in big tech and I know many people who'd love to RTO at least in a hybrid capacity.