while the two commentors above put it somewhat nastily, they have slightly good points - the main point though, is that in FE your training doesn't only affect a few skills - where you put your points has an effect on your crafting, etc - so a full respec would inevitably have to make you start your crafting all over again as well.

Whereas their current method, a few points per use, means you can back out of a bad decision, but not have your character majorly affected.