The rise of professional airbnb renters have also lowered the quality quite a bit. When a lot of listing were for apartments that the renter used for themselves part of the year and rented on airbnb when they weren't there, you could be sure to have decent bedding, etc..
Instead in professional airbnbs, there's a race to the bottom with extremely bad mattresses, uncomfortable beds, heaters that don't work to save money.
I don't think it's a decline in safety as much as a decline in Airbnb itself. Not only has it become bigger, which allows them to care less about screwing customers and be bolder at committing fraud and breaking various laws, but it becoming bigger means more bad actors (from slumlords to outright scammers) are now abusing the platform.
A big part has been life stage changes, but also I think there's been a decline in safety in many major cities, such that I just don't want to risk the crap-shoot of an Airbnb any more. Hotels are not perfect, but it's a known product compared to Airbnb listings.