Hamstrings are often tight/"angry" muscles, and they won't grow to full capacity unless it's corrected. You can bomb them with every leg curl variation there is, but they'll just lock up even more. Unfortunately it isn't always an easy fix. You can't just do static stretches for them to increase flexibility/mobility; and you can actually makes the problem worse if you do static stretches too aggressively (I know this from experience). I have to do a lot of dynamic stretching, and active release therapy (as well as other stuff) but it's been an ongoing struggle. Obviously tight glutes will exasperate the problem as well.
If your flexibility is good, I really like good mornings as opposed to RDLs. I feel them more in my hamstrings. My glutes try to take over on RDLs towards the end of a set.