It's probably to do with how replaceable the company is. It takes an actual airline or travel company to realise "oh hey we should do this" to destroy this company, they offer nothing beyond a pretty interface unless they have some secret magic behind the scenes. Maybe that's how business works, you gamble on nobody ever challenging you, but I've seen a lot of the criticism towards HM come from how replaceable they are, because they don't even have a market share.