That doesn't stop them from adding dark patterns on top. Acting with business interests in mind, airlines are practically compelled to add dark patterns. Other airlines have moved towards RyanAir's model, not away from it.
I find that frightening, as an ethical person who wants to run a business.
Lets say you have two airlines that both need to offer a flight for $300 in order to make a reasonable profit. If one shifts $15 of that cost to bag fees, then people will choose that one even though the end cost is the same. The other airlines have to follow suit or they will fail to stay competitive.
Your comment was regarding conversions and upselling (purporting it as a dichotomy to do those yet deride dark patterns), yet neither of those ever need dark patterns -- if you have a compelling pitch that makes the customer knowingly and intentionally choose the option, you have legitimate business gains.