I like etymology but this seems to be a “nobody knows” one. The term cramp IIRC goes back to medieval times but for masonry fixings rather than anything like a modern clamp/cramp, more like brick ties.
I reckon it’s basically just one of those things where a messy bit of wordage has lasted long enough that people get attached to it and start attaching mythologies to it and getting really intense about it for no reason and thinking it makes them better or smarter than other people, like further and farther. But since a cramp clamps and a clamp clamps but a clamp doesn’t cramp and everyone knows what you mean, the sensible thing to do is just decommission cramp and say clamp for everything. Of course we do not do that. the idea that the tool’s name is dictated by the job it’s used for is… mental, tbf. Oh yeah that’s a hammer if you’re hitting a rock but it’s a harmer if it’s for hitting wood and a hamrer if it’s for hitting metal.