I think the arguments are based on history and the fact that a country home requires up-keep (money, if not on a Crown Estate).
It's all a matter of what Harry can afford or is willing to use his capital on. Also, why have a
grand country home if one spends all one's time in London, and vice versa, why have a grand London home that stands idle most of the time because one is always at home in the country.
Fact is Apt 4B has been sitting idle for years and there are news articles going back to 2011 claiming that 4B us being kept free for Harry. It seems to me the decision was made long ago. Harry picked Apt 4B (maybe) but has not wanted to move in until he marries. ?
P.S. I would think, as well, that the woman Harry marries would have input into the future family's living arrangements.