According to this reply, that was not completly true 2 years ago.
Yes, the answer I linked in my reply was updated in April 2016, so it seems to be a new thing.
Twitch have decide to censor alot of games without knowing them.
I feel that you are quite upset about this. I personally do not see censoring here - Twitch wanted to ban non-gaming streams. They have for a while. And they now found a criterion what a game is - if it is mentioned in the giant bomb database. I never heard of giant bomb before, but maybe it is a good authority for the gaming culture. Twitch also gives an option how to add a game they do not know about - but you seem unhappy with that approach too.
I think, Twitch made reasonable choices for their goals and communicated them clearly. I do not see censorship or that it is reserved only for Blizzard, EA and Steam. As a a customer of Twitch, it is perfectly fine for you to be unhappy with their services and not use them anymore. However, I find it a bit unfair, bashing their decision and bad-mouthing them of censoring in a non-twitch forum - they are hard working people who just want to do the right thing. Please complain to Twitch directly, not here: it is not like Wideland's community can do anything to change Twitch's decision.
fwiw, I think Twitch's choice is reasonable, it seems well communicated and there is a clear path forward: add a Widelands entry to giantbomb.