The problem is everyone knows lions are stronger, and everyone wants to be one, and there's no downside. Look at Serge he is a pretty effective infantry, last week he was riding around on a +3 cata in full plate, getting kills like that, eventually he gets dehorsed and then fights on foot like nothing happened. Same for guys like Cyranule, San, etc. Very good infantry who dropped 4-5 easy points into riding and start round mounted, racking up kills lancing people as they move to mid of field. There is no downside at all to doing this, being cav is a huge power enhancer.
Organized infantry units just do not want to put up with this kind of nonsense, they want stand up fights not to sit around being picked off by ranged and playing tag with lancers. Most organized infantry clans are on siege these days besides maybe AoW and Hopsitaller (more of a mixed class clan), where you can actually get legit melee fights. You will find decent groups of KUTT, SoW, HoC and NH on siege most nights now, and I've noticed even top notch infantry from battle drifting in like miley, voester, galv.
Battle is becoming the cav server, and siege the infantry server because cav is so OP that people are tired of the cheesiness of dealing with it. It's too bad cuz battle used to be better for formation fighting and open tactics, but now it's basically impossible you just get overwhelmed by swarms of OP cav, and if you try and form a tight formation against them, range will feast on you.