Basketball is a job for NBA players. They workout for a couple hours per day. The they either practice for 4 hours or so or go play a game where they are tied up for another 4-5 hours or so. After that, they have real, honest to goodness lives like you and I. And since they work at night and sleep and nap during the day to be fresh for games, many, especially the unmarried ones, want to live in a city that has certain amenities.
Some want warm weather for golfing or outdoor activities. Others want a nightlife, a city that is geared toward more older adult entertainment. They want clubs that are open until 4-6AM. They want after hours spots. They want clubs with large VIP sections. They want men's clubs. They don't want not to be surrounded by college kids. They want cities where other types of celebs(music industry, movie industry, modeling industry, other pro athletes) live and spend time out and about. They also want cities that are in fair tax states because even though their primary residence might be in a good tax state, they get hammered by local and state taxes for working in other states.
Boston is way low on the totem pole for these types of priorities that might make a player swing his decision in Boston's favor. If a player can have a shot at winning and playoffs in other areas that offer this desireable stuff, why are they going to come to Boston?
I don't see Marion coming here. He seems like a guy where ego, status on the team and most of the above aforementioned availabilities that are there for him are all important to him.