I didn't downvote, but your claims could use some justification. What makes you think quality is declining? Personal experience? Second hand anecdotes? Media stories?
Personal experience. It's fairly obvious if you have been using the service for any length of time in cities like SF, NYC, LA, Berlin, Paris, Barcelona, really any large city that has banned or curtailed the legal offering of the service. The result is you have a lot more people offering properties where it is banned leading to awkward situations for customers. The listings are not permanent and get removed as soon as they receive a bad review. There are no checks on host providers at all. I actually think it is not any better than craigslist at this point.