Why don't they lean into ad blockers and making the web less shitty? Is it because the web staying shitty makes people use apps instead?

It's because with the way that the most capable adblockers are built, they can't function without injecting code into every page and intercepting traffic. The privacy implications for someone installing an adblocker extension with malicious intent (or more commonly, a formerly legit blocker gets bought and gets turned malicious in an update) are dire.

I’m sure that is a part of the reason. I hate apps with a passion…