No one is forcing you to watch the new ones. It doesn't mean that other people can't enjoy them. Making new movies in no way takes away from the originals.
No, no one's forcing me to watch them, which is why I don't. But my point is, you're arguing that the film series should be continued to attract a new crop of fans. That's a different argument entirely from "I want more stories about these character."
Why make a sequel at all then? With this thinking you wouldn't have had Temple of Doom or Last Crusade.
My point is that you do not need to make new films in order to attract new fans. New fans could, oh, I don't know, discover the old films and enjoy them for what they are. I know, novel concept, right? You don't' need a new film to get them to do that, either. If the Indy series had stopped at Raiders...honestly, I'd be perfectly fine with that. Raiders is such a good movie on its own that I don't particularly NEED the other two films even though I enjoy them.
See, here's the issue. There's this underlying assumption that more = better. It doesn't. More stories doesn't mean that each successive story will be better. If anything, more usually means worse. Sometimes it means better, sure, but it often means worse. Do you think that Temple and Crusade are as good as Raiders? I don't. Even though I enjoy them, I don't think they're up to the level of Raiders. "More" in that case, did not equal "better."
Likewise, "more fans" is not necessarily a good thing. It's not a bad thing, it's just...a thing. From the perspective of a fan...I honestly don't give a damn if there are more fans added every year. I especially don't give a damn if the means of adding those new fans is to crank out inferior product.
Now, if you happen to be a movie producer or the owner of the rights to the Indy franchise, hey, more IS better. More fans, more money, more merchandising opportunities, etc. But as a fan? More is not better.