I'm not questioning but rather curious, why are the Heavy Lance doing less damage than the light and regular versions? It is quite a lot more expensive. I guess the longer length might make up for this somewhat but to me it appears underpowered and unpopular due to this.
It was done a while ago for balance reasons (pretty much everyone used heavy lance if they were a cavalry lancer). Unloomed heavy lance used to be 26p. Then it went down to 23p, then it went back up to 24p, then to 25p (where it is now). It is still on the weak side (26 base pierce was better IMO). It is pretty balanced at the moment, the lance does way more damage however (and is a lot faster), for not a large length difference.
Personally, I think the great lance, lance and heavy lance should be priced the same. light lance should be cheaper IMO.