its not so much "obsessed" as "easy"
Whiterun is the first big town you get to, is central, easy to navigate, has decent shops and amenities, contains one of the major "guild" questlines that pretty much everyone who goes melee will want to do and from a lore pov the Yarl is an ok guy and its a kinda almost a neutral town
the house is not large or fancy but imo sometimes people like a small "concise" house better with just a few chests/cupboards to manage and a simple quick to navigate layout (personally i actually delete a lot of the stuff in the Whiterun house including a few containers to make it more minimalist)
Lydia is actually, despite some people not liking her sarky conversation, a pretty good kick ass companion and she is decently attractive (if a little butch)
its easy to see why, even when offered some of the alternatives, people decide just to stick with what they have.
plus moving house is a pain in the ass