Problem with official servers is the population can be in the 100’s so having too long of decay will have issues of clearing properties of players who quit. I always figure 8 days for official servers (non-holidays/vacation periods) would be optimal for players who play once a week.
Official servers tend to have many people pop in and out (trying out the game) or many who play infrequently (once or twice a week players). I seen about 30+ different players in a week when I pop on, while the server only has about 4-16 players online when I do log in. Plus majority of the names i saw this week were new to me. I haven’t seen many of the regulars I normally see.
Private servers may have less fluctuating number of new players joining the server, plus admins can resolve issues faster.