@Riot Why don't all melee champions have natural MR gain?

Right now there are 5 melee champions who don't gain MR by leveling

They are:

Singed Poppy Maokai Yasou Shen

Funny thing to is that there are tanky/all in champions (with the exception of Yasou whose more of an assassin)

So why not give them the 1.25 MR that every other Melee champ has. even Jayce gets MR by leveling his Ult.

Tanks are already gimped in this Assassin/Brusier meta, why not a bit of love?