They'll always be "underrated" and underused because they're so damn unenjoyable.

Sure, we all need to study and learn things in life here or there, but the flashcardification of the process makes it boring and painful.

From my own personal experience trying it, I find the process to be too far removed from the practice of accomplishing what you are setting out to learn to do. An analogy might be like memorizing a recipe by using Anki cards and not physically cooking it versus doing cooking it a bunch of times without deliberately trying to memorize the recipe. For me, the latter is far more effective because you have your 6 senses of mnemonics to memorize what you are doing. I may not remember that I need 2 cups of flour, but I remember that I scooped my purple flour scoop twice and that the white contents felt powdery like flour and grainy like sugar. Even if I forgot the recipe my body would have smelled, seen, touched, weighed the material and I have all these physical clues to work with.

Learning by doing, experiencing, immersing is more of a "repetition that you don't even know you're doing" while Anki/SRS has the feeling of a chore and an obligation.