So, we've got two possible rationales here:
- The devs are trying to keep under ~35 buttons despite even controllers having access to 48. For this reason alone, they in roughly equal parts (A) recycle abilities, giving back near-identical skills at higher levels, and (B) put out uncreative bloat or unpolished clunk that is then, at best, removed and replaced with a newer, shinier recycled or equally half-assed ability.
[I.e. controllers hold back job kit design.]
- The devs recycle abilities even while having a quarter to third spare space for the same reason they so often put out uncreative bloat or unpolished clunk: because it apparently isn't worth their bother to invest so much time over more than a handful of jobs' quality of gameplay.
[I.e., Creative bankruptcy / insufficient job developers / low perceived profitability of spending that much time on jobs' quality of gameplay / insufficient developer effort for whatever reason... holds back jobs' quality of gameplay.]
Given that the first has never come close to being the actual bottleneck, I'm having trouble believing it's the key factor here.
Claw-gripping has nothing to do with how many keys are available to you... It is only done to be able to move and look around while using those keys.