It doesn't punish the forgetful because it would be the same scenario as the current system if you forget to set your spells. While your suggestion punishes the smart, as if they changed it to lock traits after spell swapping that would effect manual spell setting too. Meaning that people that use the current system for manual spell swapping for changing traits would be the ones getting "punished".
E.G. Maybe I want to swap in/out treasure hunter during combat and only need to change a couple spells for it. I do this and lose access to all my spells like normal and then on top of that, all my traits and stat boosts too. Because some noob can't remember to use the spell swap system properly to change his spell set before going into combat?
