This is also a holdover from how older trackpads with physical buttons worked. The buttons were at the bottom, so click with the thumb and move with the finger(s).

This is how I first used a trackpad 20+ years ago and I never felt the need to change. I tried some of the newer ways to click and drag and they all seemed worse. Tap to click is the first thing I disable on any laptop, that’s what my thumb is for.