Because wherever there are people with power, there are those who will do ANYTHING to gain access to that power. When there’s no mechanism to FORCE those with power to over the law, then they won’t, and their cronies will be insulated to some degree from consequences. Enough people (Congress) who could force consequences are the ones benefiting from Trump’s corruption and could suffer negative consequences for turning against Trump. A lot of those guys are very old and extremely unlikely to suffer consequences if the following administration is also Republican. It’s a big ugly tangle and unless somebody is willing to just arrest the Orange Jackass and all his ghouls, nothing will change.