Eternal realm gear is useless because there is no endgame progression system to use it on. Non seasonal leaderboards with something like greater rifts in D3 would give the gear and chars some value.
D3 eternal realm was actually quite popular before the paragon stacking from each season got out of hand, so there was no ways players could compete even if they took the time to find the best gear. D4 won’t have that issue because of the 300 paragon cap, so D4 is actually in a better place then D3 for eternal realm if they implement the above.