It isn't a problem with game mechanics. All it takes is for 3-4 players to hang back and protect the spawn area. Cavalry that see's active resistance will very likely run off to less dangerous victims.
Unfortunately, that's also false.
As a longspear user, i stayed at spawn with two teammates (2handers), to protect the future people, and then move in a big huddle to the rest of the team. The result is, the main team lost a longspear user and two good 2handers, while raping the late spawners, with the loss of two horses and one rider. How ? Easy. Have 4 lance cav charging at you couching from 2-3 different directions, the longspear user stops one, get couchs by another one, etc...
You all blame inf for not playing smart, but smart cavalry is unstoppable. They just have to sacrifice a HORSE, and can kill a dedicated cavkiller. GK are even smarter, they use their horse archers to shoot at the longspear user "just" before he's being lanced. A longspear user holding his attack is slow, no matter the athletics, and an easy target for a good mounted archer.
I'm really a bit bored to "constantly" have to watch my back, may it be at spawn, while moving, in teamfights, etc... Ninjas were easy to deal with (oh look, they're going right, well, they won't be in our back in less than 30sec, no need to check in between). Cavs are another problem : Oh, you died, you didn't check behind you in the last 5sec, even after having watched there for the past 2 full minutes. "Have some awareness nuub !"