Why isn’t the business model scalable? The model is to write software which scales at low cost so with lots of users the fees are minimal. And it seems to work since they are profitable and made 4.8 billion last year.
One writeup about some of the airbnb issues is here: https://www.theinvisibletourist.com/why-you-shouldnt-use-air...
Any of the other gig economy setups have comparable issues. For food delivery it is now more expensive, with worse conditions for the drivers. Here in Finland unfortunately they deregulated the taxi market as response to uber (instead of just doing the senible thing of just banning it) - as a result taxi market is a mess now, and I've avoided taking a taxi or comparable services for years now. I'd rather walk.