Are there other prestigious classes, like for non spell casters, fighter?
No. What would a pretoge fighter do? They already get fighting techniques and advance BaB really well, so there is nothing left for a fighter to get as a PrC.
Originally, prestige classes WERE stronger than regular classes, and were in the DMG so the dungeon master could control access to them. Their power was balanced by both DM fiat, and by onerous prerequisites.
People also feel that paladins and rangers are sort of gimped. Why be a paladin when you could be a cleric and do the same, but better? Rangers are just Druid/fighter multiclass, with a rogue dip.
But how could we make paladins and rangers strong enough, and flavorful enough, without unbalancing things? By restricting access based on DM fiat.
Of course, it doesn't work, but worth a shot, no?