>>7d7n+(OP)
OK I'll bite. Airbnb is a website. A hard-to-navigate, overproduced one, but it's still basically just a website coupled to a database. And it's not even as complex as Uber's because it doesn't need realtime GPS tracking of anything.
Airbnb is investing in their business, in what they believe (and they probably know from their numbers) will grow their future. They don't have to rationalize it only if there is complexity involved.