> ..sometimes even crash

I don't think this is the case. Either way you might get one crash per millions of loaded ads. Making this argument just silly.

Not sure if you write software or not but crashes are more or less expected, just keep them below X% and it's "ok".

I'm not sure I agree. Depending on how we define 'crash', I've certainly seen ads render pages unusable or prevent my access to content. Infinite request loops, script crashes that take down desired video content, improper loading covering content, and more.

The obvious example would be sites with mediocre mobile pages fighting to serve ads. It's pretty standard to hit broken redirects, script issues, and all sorts of other crash-like behaviors visiting those.