Because there are no alternatives. It's either fast travel, walk, or ride a horse. I mean, what ever happened to travel services?
The argument "If you don't like it, don't use it" doesn't really work for Oblivion. Especially when most quests assumed you'd use it, and, like I said, there were no realistic alternatives other than walking it riding a horse.
Agreed.
It annoys me when people say "If you don't like it just don't use it.". That's kind of difficult when the whole game has been built with the ability to fast travel in mind - which puts you at a huge disadvantage if you don't use it.
Anyway, what about a more daggerfall-esque fast travel? Where you can go anywhere, but you can adjust whether you will go be foot/horse/carriage/boat, choose whether you lodge at Inns or camps, or travel cautiously or recklessly (all of which influences how much your trip costs, how long it takes, and whether enemies might interrupt your journey.)
It seems simple enough to implement and would greatly improve the fast travel system, but still appeal to a large audience I think.