Mine goes back very far but can hardly bend forward, didn't know it wasn't normal until my wife pointed it out.
Hers goes almost 90 degrees forward and only straight up and down going back
Being able to bend backwards is genetic, and at the extremes it's commonly called this:
https://en.m.wikipedia.org/wiki/Hitchhiker%27s_thumb
I haven't heard of your case where you can't bend it forward. Does it hurt or cause any discomfort if you try to move it forward (without help and also with some gentle pressure)?