Mastery is all about usage. Lance and Spear may "look" similar, but they are used in fighting in totally different ways. As are Short Spear to Long Spear.
Lances are typically used from a beast of burden (Horse or other). where a Short spear is used in melee combat and has a very active fighting style (Turning, thrusting, and even swinging), Long spears are primarily thrusting-only weapons used in circumstances where you have a "Shield Wall" (one or more characters standing in front of the long spearman, where the spearman can attack through their position to attack targets on the other side of them).
Even when you get into Swords, a lot of them are Similar, but their fighting style is specialized, and is what the master has learned...