Because some fans are batshit crazy that's why, plus would like being swarmed by people that adore you 24/7 add that onto being under constant watch and surveillance by the media to see if you do anything wrong and if you do you are thrown out and massacred by the media.
Most are just over paid over rated narcissists who don't deserve people's time and admiration. Most of their image is 99% marketing hype anyway. Forget them, find someone who deserves your time and effort. Friends, family, boyfriend.