Yes I know that but that falls under Copyright Infringement and the owner could possibly sue Steemit.com for you Posting his/her Video.
It's us who have to stop or else there won't be a Steemit.com for us to write Posts on.
Now you may say that Steemit is Decentralized and nobody can stop it. Then you are wrong, Steem Blockchain is Decentralized but Steemit.com is very much an Entity which can be closed under Copyright Infringement.