Yeah, but it's not like they gave Snoke any character either. He was just kind of there, and then he wasn't. Also, it's pretty unrealistic for them to expect the average viewer to turn to extended universe stuff for explanations of major plot points that should've been in the movies in the first place. They don't even need to go into great detail. It's not like anyone is asking to see Midichloreans or a galactic senator fillibuster a vote on trade resolutions.
Literally 1 short line of dialogue in each movie could've put 90% of the complaints to rest, they didn't have to have a "reveal" scene with music swell and gravitas or anything
One bridge officer says to another "where'd they find this guy anyway?" "You didn't hear it from me, but...a ship floated in from the outer rim, badly damaged, with only one survivor aboard. They say he was only alive from sheer will alone, or from his mastery over the force. Either way, The First Order owes our existence to his tactical genius, so never question him again, is that clear?"
Or Luke says "we thought all the old Sith masters had been defeated...we were wrong. We don't know much about Snoke, but he came wandering out of a ruin on Balthakk a few years ago and has been a force to be reckoned with ever since."
Or Kylo says "I know you owe my former master Luke a debt of vengeance for that wound he gave you on Parthax" and Snoke chokes him out and yells "never speak of it! I will settle my score on my own time."
Literally anything, for 5-10 seconds, in two movies