I can't speak for FB. But I know a local (non-US) real estate company which does crap like this (they also love to disable right click and detect when browser tools are open and programmatically close the tab/page when that happens), and they're not paying much. I'm guessing it's double of minimum wage, which isn't high here.

Knowing what total comp is like for those companies, I'm sure Facebook more than exceeded the price one might put on ethics.

I've personally resigned from positions for less and it hasn't cost me much comfort in life (maybe some career progression perhaps but, meh).

Shouldn't this kind of thing be illegal as a matter of accessibility?

Can you link to the law you're talking about?

Since this is about something nobody wants to see (ads) my guess would be that it might be legal here.

They say that they feel like it should be illegal. And you ask for the corresponding law, calling it a legal argument...

Can you genuinely not see the disconnect here?