Sure, I'm on both sides depending on the situation so I can help here.

"Collaboration" and "communication" are definitely issues, as employers state openly, but not for the reasons you think.

I worked in a fully remote company for the last three years, I selected people who I knew would be independently motivated and who knew how to communicate effectively in an async manner.

Yet, there were issues still in communication that would have been solved with being able to hear someones tone and body language. Little issues spiralled out of control- and lack of trust crept in when people were quietly doing work that had very small visibility (but was important).

I'm not saying remote work was the reason, but remote work exacerbated certain particular issues in this dimension- eventually the founders (who had lost trust) started laying off people they perceived as not important, despite them being fundamental to any future in which the project would be successful.

You'll also notice that the companies that care the most about RTO do not invest in communication in other ways, they'll probably use awful communication software like Teams, WebEx - or in marginally better cases: Zoom.. and since people don't like to interface with these tools (and they're poor even when you do): there can be a feeling of being out of the loop from upper management as they don't know what's going on.. they just see radio silence.