Because people don't behave in a hotel as they do at home - they're on holiday after all, so they might come back late drunk, they might want to party, they might make a mess in the hallway. Different people, every night. An unlike an owner, they could be anyone, or bring anyone with them. Basically, you are externalizing all the downside onto your neighbours, while pocketing the upside. It is no surprise that AirBnB started in America.
Upvoted to counter the downvote. US citizen (who went to college in Europe) here and I agree that it's no surprise that AirBnB started in America. I've seen ruthless business practices all over Europe, but there is always a level of social responsibiltiy that is more generally lacking in the US.
Edited to add: Americans almost always say "vacation" instead of "holiday" but you could be a long term expat who is picking up the local language.
