First you waiste skill points on horses,second horses are not cheap to buy and maintain,horses die from 2-3 arrows or 1 bolt,or from one hit with any 2h/pole weapon,if you use plated horses other lancers or HA can easily cach you and you can't run that easily from them,you are more exposed target when you are on horse,and you need to use crappier gear unless you are filthy rich.
i am light cav-lancer and i use reinforced haumbergeon,sarranid mail boots,guard helmet,crouser,and lance i stated with 80k gold and i have now 110k,so i made 30k in this generation.
Now compare with this i was infrantery 2h and i used bascinet,haumbergeon,mail mittens,war cleaver/great sword and sarranid mail boots and i made 300 000 gold in one generation.
i am light cav i make money,but heavy cav can only lose cash.
I am also very lucky cuz my horse brakes every 4-5th round,but sometimes it brakes 5-6 rounds in row. if i play with war horse only one map i get back to 80k very easily.
There is now a lot of cav,but there is not that much good cav. You can only see 2 Chase and some dude on A that are always first in scoreboard,but other cav is just in middle or bottom of scoreboard.