They blocked wiki at your school because the kids going there are too dumb, and don't understand that wiki is not a source. It's an aggregate of sources and you have to find the source which contributed to the wiki page information you are using, before you can cite anything.
We have a tail of two towns where I live. In one, the Hurricane Katrina kids overran the place in 2008.
From 2008 - 2011 they took the entire towns testing averages and threw them in the toilet. Apparently they don't teach them shit down there. Add to that, these kids couldn't understand that wiki was not a source, and would actively argue with teachers about it. Even when the teacher was giving them the answer to the problem they had, and trying to teach them how to source information correctly. I specifically remember my brief time going there, "psk, teach you don't know shit... wiki is a source, it's got the answer right f**king there."
Just a bunch of class clowns is what we got fro some reason.
Anyways, the other town just to the north, is the town I ended up going back to school at.
They were not tolerating the Katrina kids behavior, and life is tough we aren't changing everything cause you had a hardship. Many actually got expelled, and I have to wonder to this day... wtf was in their water in Florida?
Anyways, these kids were made to listen or made an example out of here. At this school, the teachers will not give you the answer. By that I mean, they just say, "Wiki is not a valid source, I will count off if you cite wiki."
Nothing more than that. Leaving everyone to avoid Wiki entirely.... cept me, and anyone else smart enough. Cause it was never blocked. They merely did the right thing and made it a part of our grade to show some self-control, and do the right thing. Regardless, I got on Wiki one-day for a paper on Komodo Dragons. Teach walked up and said, "You can't use Wiki, you need to back out of there."
I turned to her and I said, "I won't be backing out of this website, because I'm not using wiki."
She stood there for a while and watched over my shoulder, as I showed a moron teacher exactly why they had been told to say what they said, and why Wiki isn't blocked at our school.
TLDR:
Wiki is blocked because your school is full of morons. Either staff, students, or both.