Idiotic plays

I've recently come across some really stupid plays and I started to wonder how much these cost to the player.
Few people tend to, without exception, stand on soft hands above 13, fail to split aces, split 10s and double on 12 and 13.
Does someone know how bad these plays actually are?
I know splitting tens vs. 6 is justified on high counts, but the split happens more frequently vs. dealer 10, so seriously doubt these people are counting or using camouflage etc.