It’s probably to reduce exploits in un-intended power gains etc, I used to do it with gear stats, when they made it MS only, to make it like it used to be using alts to roll alt specific MS.
Can’t do that anymore either unfortunately. That said it was a pain so idc too much and if it’s meant to be in the game, I should have access to it, from that character.
It’s probably a good thing long term, even though it sucks short term. Becasue what we really want is choices, but those that are balanced and inline with the games construction.
Ultimately i would want that to open the doors for things like dual profession type gearing to become available. Can’t get there if there is too many exploits etc.
Or they just nerf the fun for reasons, IDK, honestly sometimes I am not following this game at all. Too many classes I guess are starting to feel the same, which i predicted would be the case making it too much like D3, the identity gets lost since they can all do the same things.
That said perhaps it always was there, just lost in the affix bloat.
But class specific tempers will fix that.
So Since they caught on with gear stats, I would guess that you need not worry the gear wont be equip able if you use alts to run class tempers for other classes.
Only concern I have how long before we get more and better tempering options to fill the void.
It’s still hard not to miss things from older diablo, like dual profession and magic gear with req and charges like a warrior can use a staff for a bit and that sort of thing if they have some ranks in magic. 
