Why the constant tinkering, Devs?

[Borror0]

But you still have spells they are changing that the babysitter can't protect you from.

I know but none of those really make the game easier.

How does tinkering make a game not go stale?

Buy A Theory of Fun for Game Design and read p. 44. Koster explains itfar better than I could dream of. Basically, by always changing patterns, you prevent players from groking how the game works fully and thus prevent them from getting bored.

Another way of looking at the question is asking yourself why new content keeps the game "fresh".

And this...this is only true if you play the game exactly as Turbine designed it to be played.

Turbine are designing under some assumptions, yes, because they cannot develop the game while covering all possible scenarios. It would just be unrealistic. So, yes, some changes might have different effects outside of expected gameplay but that's just how life is.