I think if anyone does care it has to do with why they watch people in movies or how they want to relate to the talent they see in musicians.
If you're only interested in a musician in terms of his or her talent, it doesn't matter what their sexual preference is. But what often happens is that people (especially women) fantasize about musicians and actors romantically, so that the discovery that someone is gay and wouldn't reciprocate those romantic feelings or fantasies bursts their bubble.
In acting, it depends on what the role is. Because part of the reason I go to a movie is to be transported into a story for a while. If the people who are telling that story or portraying characters aren't believable in their roles, it doesn't work.
And sometimes people make such an issue of their sexuality in real life that they essentially typecast themselves on the screen as well. What you know about them offscreen indelibly effects and/or overrides what they're trying to portray onscreen.
It's a shame that's true, but it is. Although there are some people who are so talented at what they do that you're just happy to be able to listen or watch what they do, sexuality doesn't matter as much.
For instance, I really like Michael Stipe. Don't ask me why - usually I'm more attracted to really masculine types- and he's definitely not that. But when he writes and sings, he's such a talent, I don't notice his lack of masculinity.
And I like how he labels himself - he calls himself an 'equal opportunity lover of people.'