Einstein got his Nobel price for his work on the photoelectric effect (basically a small part of what became quantum mechanics).
Special and general relativity were too new and revolutionary (and admittedly strange) so that at the time, safer bets were considered for the price.
The strangeness hasn't gone away, relativity does still take some getting used to, as does quantum mechanics. But all of those are proven scientific theories backed by experimental and observational data such that they are accepted as true within the margin of error for the corresponding data (as always in science). All predictions that could be tested stood true, we just have some predictions for extreme cases that are contradictory and currently not confirmable by experiment or observation.
Scientists, even back then, with time and data, came around to accept relativity.
Dark energy isn't like that. Dark energy is an observed problem in cosmological data we cannot explain. The expansion of the universe in some phases of it's development is faster than it should be. When we plug that data into our current cosmological theories, it looks like the energy content of the universe is higher than it should be by observation. Because it is energy and have not been able to observe it, we call it "dark energy". Explanations such as "the data is wrong", "the theories are wrong, here is a different one", "gravity is different, try this alternative to general relativity" and stuff like that haven't yielded any satisfactory theory that would fit the observations. So we are stuck with this problem called "dark energy". We haven't solved it yet.
Basically we are like before 1900, where there was no quantum mechanics, just some strange experimental results that called for a new theory that somebody had yet to invent.