@Sally895
I don't really blame the guests as Airbnb does not explain it to them clearly, or even misleads guests as to what the star ratings mean, but anything less than 5* on Airbnb is BAD. Hosts are told they must maintain an average of 4.7* or above as a basic standard. If a host gets a 3* review, they will get a warning. If they get a few 4* reviews, they will get a warning.
So, can you see why a 4* review is upsetting to the host? If the listing was not clean, if the host was not responsive, late for check in, or the had misrepresented the listing in some way, those are reasons to knock off stars. If you booked "an economical meeting place for a couple of nights," and that is what was advertised and what you got, there is no reason to knock off stars just because that economical place was not the Ritz! The Airbnb rating system bears no relation to a hotel star rating system.
Unless something went wrong with the stay or the listing was misrepresented, which it doesn't sound like it was, then it's not actually fair to leave 4* or lower because that can really hurt the host and they gave you what they advertised. I am surprised that as such an experienced Airbnb user, you would not have known that already.