I've had the same experience in major American cities - hotels being cheaper than AirBnB - but only when looking at full apartment rentals on AirBnB. You can (obviously) usually rent a couch cheaper than a hotel room, but that's not really comparing apples to apples.

That being said, both AirBnB and hotels make it difficult to compare their prices "apples to apples" as hotels tend not to include taxes and service fees in their posted prices / AirBnB tends not to include cleaning fees (last time I checked)