I think that's basically true but it's not a conspiracy - take Apple, for instance. They have a $5 billion HQ on their balance sheet. If everyone works from home, then their investors will ask the CEO "why aren't you using this asset that costs $5 billion? It's inefficient - sell it off."
The problem here is that if the CEO sells off the HQ (in a market where everyone has a bunch of unused real estate) they'll almost certainly take a loss (and potentially a loss of billions of dollars, if they e.g. can only sell it for $3B), whereas if they keep it then it's technically valued at what it originally cost to build. The CEO's job is to make the company (look) profitable, so the CEO wants to find any excuse to use the HQ, even if it loses a bit of money or doesn't otherwise make much sense.
For companies that lease, it's the same problem or even worse - corporate office leases tend to be e.g. 3 years, and they're locked into paying actual dollars every quarter until the lease term ends, so if they can't claim to be using the office space then they're directly losing cash. Renegotiating the lease is a bad bet as the landlords have basically zero incentive to do so in the current environment. Thus, they want to appear to use their office space.
There are some other niche benefits too - forcing return to office is a great way to reduce employee count without needing to claim you're downsizing (although if you want to downsize then you can totally make the claim), and it makes office perks more valuable.
There are also some tax breaks from local governments that are contingent on having X number of workers in the office, and WFH could potentially require reversing the tax break.
None of these are "conspiracies", they're just sparkling incentives.