They usually do not just fill a hole in a theory but make a ton of new predictions that then can be verified.

Conjecting that the earth is round did not just explain why ships disappear behind the horizon. It also predicted that you can get back to point A by always moving away from it and many other phenomena.

Since it was first used to explain galactic rotation curves, predictions of seeing the signature of dark matter, in the CMB, in gravitational lensing observations, in the structure of galactic clusters, the expansion of the universe, etc have all held up.

And these not only are consistent with the existence of dark matter, but roughly indicate the same amount of it as a fraction of mass in the universe.

So I disagree strongly that the existence of dark matter hasn't led to other predictions. Indeed, the number of different phenomena that lead to it is one of those things that have made alternative theories so difficult. There are a ton of alternative gravitational theories that can explain one or two of the above phenomena, but trying to match them all (and not contradict other observations), seems to be somewhere between difficult and impossible.

That sounds interesting. Do you have links to some of those predictions and how measurements held up?

There are lots of verifiable dark matter predictions, just none of them have been verified yet. The article mentions some of the predictions around WIMPs. It's not like string theory where there's no way to disprove it.

I like to repeat myself on this, but proposing "invisible" matter has historically been a very successful strategy in fundamental physics. Simple laws have a tendency to stay simple.