That's because you can't have people permanently maiming each other during "friendly practice". If the village parents send their kids to the local monastery (or school, or wherever) for "training" and they come back with broken bones or just one of two eyes, they'll be rightfully very angry with the teachers of that martial art.
Hence, over time, every martial art accumulates restrictions, formalities, and the standard moves become just the safe ones. Grapples, deflections, etc...
A true "martial" art, the type optimised for maximising your chance at winning a fight to the death, cannot be taught safely in classes. Eventually people will get hurt. That's... the point!
People bringing up MMA are missing this: Even MMA has rules, and lots of them. If it was truly unlimited, very few people would escape without permanent, ruinous injuries.
What girls are told in self-defence classes is this: Go for the eyes, throat, and nose. Kick your opponent in the shins as hard as you possibly can. Knee men in the balls with full force.
If you did any of that even once in any formal training or competition, you'd likely be kicked out.