That's the basic crux of a lot of American TV, so it shouldn't be too difficult to see why people would stop liking a show. Most shows go on until the ratings no longer merit the continued production, and this is usually because the stories and characters have become so diluted that they no longer have the spark that originally captured people's interest in the first place.
I mean, yeah, there's the context of this movie essentially being a sort of trolling of a mogul who controlled most of Hollywood at the time and it also sort of gives you a window into Orson Welles' life, but I think it's still a fairly solid and enjoyable film beyond that. Visually it's just this very dynamic piece of work that has shots (the arching down shot for instance) that continue to be impressive even compared to a lot of films today, there's a craftsmanship in there that's been lost. The opening of the film is something I could see people getting a little lost with, but it actually does a fairly good job of pulling you in. To me it's not a really good film in the artistic art house sense, it's quite an entertaining film in general and I've always found that it stands the test of time pretty great.
Either way, it can continue to be an influence because it influences film makers who influence film makers who influence film makers, so a lot of it sort of ties back to it. And in general, a lot of people do go and watch it and still find themselves being able to draw influence from it. Yeah, you shouldn't like a film just because it's a classic and it's forced on you, but at the same time, I think a lot of them are classics and influential for a reason. I think people should just watch those films whenever they get the urge to because then the perspective is probably going to be their own, not marred by bias of having people tell you it's a classic you should love.
There are a ton of classics I don't like, Casablanca, The Wizard of Oz, and Gone With the Wind that I don't find myself enjoying a lot while I think something like Black Moon Rising can be considered classic, but I think Citizen Kane is probably the definition of what a classic film should be.