The dark pattern part comes in with how it's impossible to know if or when any of that stuff is actually included in the ticket price, letting airlines like Spirit list 'ultra-low' prices that end up the same or more as other tickets once you actually include the basics like 'having luggage' or 'tall people getting enough legroom to physically fit into the seat'.
Pretty much a BS clickbait headline that doesn't comport with the facts in the article:
Yes, airlines have done a ton of "unbundling", but lots and lots of people want to select their seats, check their bags, buy food, etc. and are willing to pay for it, regardless of website design. I'm not arguing that airline websites don't use dark patterns, just that it's ridiculously insane to attribute all ancillary revenue to that.