As /u/CGagenator said, lances - broadly defined - were used extremely heavily throughout the period. At the risk of being pedantic, there's a discussion to be had about what exactly a lance is. Is it just a spear used by a cavalryman? Or is it a more specialized weapon, distinct from those used by footmen?

As /u/Hergrim can tell you, specialized cavalry lances developed fairly late in the period, probably in the 12th-13th centuries. Prior to that time, knights and other horsemen seem to have used weapons more akin to infantry spears. This is because cavalry tactics changed over time. In the 10th-11th centuries, and probably well into the 12th, knights frequently threw their spears before closing with the sword (or another spear). This (among other factors) made a shorter, lighter spear favorable. Over time, the charge with couched lance became the favored form of mounted warfare, which was helped by a longer, heavier weapon.

Lances were incredibly widespread throughout medieval combat, so I’m not sure exactly where you are getting the assumption that they weren’t. The word lance refers to both the long weapon associated with cavalry, as well as the formation that many cavalry units used.

They were used extensively in medieval tactics all the way up to invention of wheel lock firearms, however the lance saw use use through the Napoleonic war, Crimean war, and even WWI. Foot infantry with the longest pikes and spears were used to counter the lance, and once the lance had broken a sword was often available to use.

The Bayeux Tapestry shows lances in battle, the Charge of the Light Brigade involved the 17th Lancers (and not just a name but actually lances), and WW1 photos exist showing lances on mounted soldiers (although the cavalry in WW1 had little impact