No geographic ties in US pro sports. Clubs can freely move, although it's a somewhat cumbersome process and can engender a certain amount of ill will.
Much of the dance re. possible franchise relocations is based on clubs' desire to get municipalities to foot the bill for new arenas. Notwithstanding the fact that all objective economic studies have concluded that public money spent for such purposes brings no real economic benefit to the spending cities, many communities without major pro franchises are eager to shell out bucks to attract teams. In turn, teams "shop" such bids in order to extract economic concessions from their home municipalities. As a result, surprising numbers of cities dole out taxpayer revenues to build lavish arenas so as to "retain" their home teams.
In the current case, (IIRC) Seattle and the state of Washington seem (bully for them!) unwilling to spend taxpayer money to build a new basketball arena, so the dance has gone on longer than it often does...