I mean it's basically an extremely high-stakes version of the (possibly apocryphal) Upton Sinclair quote: "It is difficult to get a man to understand something, when his salary depends upon his not understanding it."

Most people (at least the people I've talked to, which admittedly is somewhat of a lefty bubble but I think even more generally) agree that companies getting to or close to "monopoly" status is a pretty bad thing, and that they should be broken up. Political candidates get a lot of social credit for claiming that they're going to do exactly that. The moment that they actually get into a position where they actually could do something about it, they suddenly remember who their campaign contributors are, and can then create reasons to avoid actually solving any of these problems.

Very occasionally we have successes in this field, like the breakup of Standard Oil and AT&T), but of course both of these sort of became toothless since we basically allowed both of these companies to re-acquire each other and form the same problems again.

There are similar reasons as to why politicians will occasionally push for regulations to not allow themselves to invest in companies that their policies affect, but somehow manages to never get through.

Politicians are very rarely punished for breaking political promises, but often rewarded for making the promises. They are also rewarded by their corporate overlords for breaking these promises.