Resources, even at a semi-large company, are finite. Teams have limited head counts and usually an ever increasing list of asks from Product team. Being efficient is not optional.
Lets do a little math. FB has 25k employees. Lets suppose they pay everyone a million buck. That is 25billion. Their gross profits were 35 billion. They can afford to have two teams or 3 teams or 4 teams working on the app. I don't know what Airbnb's numbers are, but I am sure they can afford to have multiple teams.