It's a dumb conspiracy theory at the macro-scale, and the overlap between CBRE or JLL and a company's board is minimal

None of these articles prove your argument.

Did you read them?

It is, but I’m curious about why it’s so popular. Is it a Musk thing?

It's an HN+Reddit thing.

The userbases overlap significantly now.

To be fair I think the only reason the conspiracy even exists is because, apparently, nobody knows what RTO is really about. IMO it's mostly just a power play and insecure executives, but they won't come out and say that of course. We're left to speculate, and naturally conspiracies thrive.