I think you're massively downplaying how much of a hit this will be.
Let's say you make $100k/year. Think about the lifestyle it allows. You've just been informed that it's now going part time, and you'll only be making $15k/year. How far does that get you?
Now, you're expecting someone else to pay for that advertising spot, so it won't be that bad. But who is even eligible? Microsoft's Bing is the obvious answer, and probably DDG. The rest of the default search engines aren't even general web searches.
Do you really think that either of them are going to pay any significant amount to be the default? Especially when most people are going to change it back to Google anyway, since these are automatically people willing to change to a different browser?
Sure, they might be willing to pay something. But it won't be anything close to what they had before.
It would be interesting to see how that plays out in court. That clip shows that the CEO himself is aware of the concerns, and refuses to address them. It also implicitly acknowledges that the reasoning was because of those issues, and not a conspiracy to harm ex-Twitter.