Because it's destructive to the economy. The only winners when this happens are the execs who arranged the deal, which is why Twitter's execs pushed so hard for the Musk deal to close even though the outcome was going to be bad for everyone else.
To put it another way - a lot of businesses would still be operating and a lot of people would still have jobs if LBOs were illegal.
Have advertisers ever completely pulled out so abruptly from such a large platform before? If they notice that their revenue remains within forecast intervals, perhaps they will realize that their Twitter ad buys were doing nothing for their bottom line, and investigate whether ad buys on other platforms are similarly worthless.
In a capitalist system, of you want a surveillance network without saying you want a surveillance network, saying "it's for marketing" is about the path of least resistance.