Well in terms of rhetoric, and terms of persuading people with ethos logos and pathos (ethics, logics, emotions), it makes sense as to why someone would like his videos due to his illness. It appeals to pathos, or the emotions of a person for feeling bad for him, so they are more likely to 'like' his videos. Also, he enjoys his content, and people always like to see people in it for the fun rather than the fame.
He may not realize it, but his videos do appeal to pathos.
Also, due to his illness, he is more prone to haters. Haters = viewers / commenters, and people who like his videos will rally around him and try to 'neutralize' the haters, thus being a viewer/commenter themselves. So now the views and comments will rise, and as I said before, people are MORE LIKELY (doesn't mean every single time or person) to subscribe to him.