Ad hoc, accidental communication simply doesn't happen in remote work environments.
Coffee breaks are a shockingly productive element that simply work better in person, at least in my experience (and this seems to be a common sentiment at my software company).
In-person conversations don't have technical difficulties, there's much better engagement which allows people to better read the audience and adapt presentations/design conversations appropriately.
Surveys among colleagues seem to agree -- hybrid seems good, remote only simply is not as productive nor enjoyable.
This raises two obvious questions;
- Were those things definitely happening in a way that actually benefits the company, or were people simply assuming they're happening?
- Why can't those things continue to happen in an environment where people work remotely?
Without satisfactory answers to those questions it's impossible to assert comms and collaboration are actually reasons to return to the office. For example, my experience of remote working (many years before lockdown, and during lockdown) has taught me that informal comms actually causes more ambiguity and moving to remote often means people are prone to "over communication" where they leave very little out. That has led to pain for some because there's a lot more email and messaging to deal with, but it also means everyone has a greater understanding of the project. Overall I'd argue that the 'formalization' of comms on a project that comes from everyone being remote and asynchronous is more of a benefit than a cost.