What is really crippling the progress of string theory?

The fact that it's not a theory, and all the work on it has already given up on following the scientific method in order to arrive at a real theory. The entire matter is really a coup inside the theoretical physics industry, where a bunch of worthless mathematicians took the lead, and all they do is sit around totally absorbed in their math, oblivious of the previous need for, oh gee I dunno, RUNNING EXPERIMENTS to test hypotheses in order to ultimately support a real theory.

Personally I suspect that the entire physics industry just matured and found itself looking for the easy way out. Physicists were unable to find a link between relativity and quantum mechanics, despite decades of trying. So they were looking like fools. String 'theory' gave them the opportunity to work pretty much forever on physics without looking like fools to the common man for their inability to actually come up with a workable theory. Job security, forever. The new paradigm in physics is that you can sit around and play math games and never actually spark any experiments or verification process of any sort... and you still get paid your salary and your grants keep getting funded. *But there are no results.*

Hell, that's the dream of K-12 unionized educators in public systems, and they achieved that dream a long time ago. They get paid for no results, or results that are so piss poor that rational socio-economics would have fired all those people and blacklisted them from the industry due to their massive incompetence.

Anyway, to day, string 'theory' has produced no predictions, and in fact is unable to produce them, be design. It's not a theory; it's a way for about 1500 physicists worldwide to collect paychecks even though they don't actually produce. We've about the same number of string 'theorists' today as we did in all of physics when Einstein was working in the Swiss patent office. The industry became bloated.

>>5

since there is an effect in the universe that must be accounted for

Or in other words, something didn't obey the dominant theories. So in order to save those theories, they invent some gobbledygook that isn't detectable in any way and that doesn't affect any other theories, but saves that one theory. It's like if I couldn't find my underwear and made up some invisible dwarves who stole it.

but the effect still exists

But the effect does not imply the existence of dark energy except within a particular theory. Change the theory and there will be no need to invent any dark matter. Inventing made-up things which cannot be cross-checked by unrelated experiments just to satisfy the dominant theory wreaks of dogma, not science. Neutrinos were hypothetical particles invented just to save the laws of conservation, but eventually they've built detectors for them, so now we can talk about neutrinos as real, tangible particles, and even give Nobel prizes for discovery of their mass. But where are detectors for dark energy? What proves that it's even a thing and not a mathematical artifact?

in ways that suggest they have far more matter in them

Once again, they suggest that only within the current consensus theories. Change the theory, and there won't be anything to suggest any "dark matter".