Drugs which are backed by many, many studies, and yet are only around 25% effective after 2 yearsFirst things first: Don't you think that if we had better drugs for whatever you have, that we wouldn't go with that in general? (I know there are exceptions that say that we wouldn't, but these are exceptions).
Second: 25% effective is better than nothing. I have MS. The first real drugs - all injections with plenty of side effects - were around 33% effective or something like that and might have reduced severity of the stuff it didn't stop. This wasn't after 2 years, this was the out-of-the-box effectiveness.
And it was still worth it. This is because an imperfect solution is better than no solution whatsoever. Know what happens in MS when you have fewer flares? You have less risk of permanent damage. It meant your risk of bad events is less. You have less chance of not being able to walk or not controlling your bowels or having full vision.
The drugs were imperfect because our knowledge was (and is) imperfect. That was the best we had at the time. But then again, it was the foundation for modern drugs which are more effective (and easier to take than an at-home injection). Cost is still an issue, but single-payer systems still pay for them because the overall cost is less than the cost of unchecked disease.
Most, if not all of the diets advertised for MS have not proven themselves, despite the claims of the folks writing the books (most of which have had other interventions and might have just been lucky with their disease progression, like I have been so far).
TLDR: An imperfect drug that helps a little is better than no help at all.