I don't actually travel much, and have never used Booking.com. So no dog in this fight. But your question is pretty much my point: if people aren't going to use some other service, it's a lot harder to quantify long-term negative impacts of dark patterns vs the measurable short-term lift.

[Edit] There's only so much conversation to be had around a point like "we don't want to become MySpace." If what they are doing generates more revenue, and if people don't get so annoyed that they'll use another service, and if they avoid lawsuits and regulators...

You'll never hear this pitch in an executive meeting: "I have an idea that will reduce revenue X% with no quantifiable long-term benefits."