I think in many of these cases, they know from the beginning that they can't do better than the original. That might make the difference between more good remakes and bad remakes. There are a few where they want to remake them to bring them more into the future with better special effects, and perhaps better acting, and a bigger budget...and then are ones where the old one, even if it's a bit old, is actually still really good, and they'll anger a lot of fans of the old one.

Redoing an old show as a cash grab doesn't work. Or at least it doesn't work the majority of the time.

Redoing an old show to try to do it better only works some of the time. There is still a good chance that things won't work out.

And yet for some reason it seems like execs think that a remake is a safe option, rather than choosing a unique script.

Of course, there are unique movies coming out all the time. Some of them are really good. Yet they don't put their advertising budgets behind them, so you might not have even heard of them.