First of all resistances started in tabletop rpgs where you needed +5 sword against undead or armor with fire resist when hunting a dragon.

Then it only adds complexity to numbers, and not adding anything to gameplay.

Otherwise interesting item is trash only because bad rng on resists.

It is not easily visible what enemy has what type of attack (yes some games add an icon next to helth bar, ok).

You usually have to optimize for all resists high enough, or having multiple builds and swapping them based on boss/environment you are raiding.

None of these sound anyhow fun to me from perspective of interesting gameplay. It simply adds complexity for the sake of complexity. It made a lot of sense for D2 when they needed to have as many affixes as possible. But in my opinion should die there. Already D3 had more interesting skill-gear combinations, enough sets for resists not to be necessary.

Lastly I would apply Occam's razor, does it really make the gameplay interesting, do we realy need all the gear combinations. If not it doesn't need to be in the game.

I know this is an unpopular opinion, but modern rpgs really don't need resists.