Fair use is not a blank cheque, in particular it does not cover a whole play through just for the point of showing it.
Youtube as a company can have stricter standards, they could delete all videos that contain the letter "e" if they wanted.
YouTuber that use game footage just as background are really on thin ice.
...the fair use of a copyrighted work, ... for purposes such as criticism, comment, news reporting, teaching (...), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include:
1 the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
2 the nature of the copyrighted work;
3 the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
4 the effect of the use upon the potential market for or value of the copyrighted work.
