The laws are very strong. Back in the day, they would block a merger if it affected 7% of a market, and vertical integration was a big no-no. None of those laws have been repealed. The enforcement guidelines were weakened during the Reagan administration (a big factor in the rise of e.g. Walmart) but they're still strong enough to block plenty of mergers and allow the occasional Sherman Act prosecution. I agree with you that it's a lack of political will, but politics has been very unpredictable lately.

A weak law is not the same as an unenforced strong law.

An unenforced strong law can become enforced essentially overnight and wipe out those violating it.