When you go to the Cinema you say movies (plural) because it is Cinema 12 or 20. Movies is plural because you have 12 or 20 or how many ever choices. Not just one movie, but multiple movies at one location.
At Nationals it is plural because you have 10 different weight classes with 33 wrestlers in each. Plural times plural. You have multiple matches in each different weight class. so you say Nationals. 10 different Championships.
At State it seems like it logically should be the same as Nationals.....plural times plural.....so should be States to continue the logic. However logic can be consistently inconsistent. Kind of like E after C. Which we all know is the absolute rule. Always consistent.
Except............
Not sure I have ever heard anyone refer to it as States before. Might be a regional thing.
Quite often as parents you would mostly be interested in your own child making it to state and hence the singular. You are concerned about them in their weight class and refer to it as them going to State. They only wrestle in one weight class, hence no need for plural. This is entirely consistent............
unless you have twins of course......