No judgment here to those who did, but during the pandemic, several people, including several software engineers, took the opportunity to work multiple jobs. Notably, at Equifax, which is probably the worst place to do it because they have records of most people's employment. https://www.businessinsider.com/equifax-used-itsproduct-to-f...
This is the main reason. Management doesn't want you pulling 2 salaries, even if you could, so they are trying to make it difficult so you don't even try.
In addition, if WFH becomes normalized, there is a lot of debt floating office buildings in major cities, and there will be a great renegotiation. This is really bad for senior management, the stock market, transit systems and the budget of most cities. So most people that manage you and manage your managers are aligned against you. https://nypost.com/2024/08/02/real-estate/huge-midtown-offic...
Lastly, and I'm only mentioning this because I think it needs to be said, but I think that most people who are pushing WFH are short sighted. If it is proved conclusively that software development can be managed and completed remotely, then it will devalue your labour as you are forced to compete with smart people in countries with significantly lower housing and energy costs. Anecdotally, this is already occurring.