Usually on YouTube there are top comments that you can vote, and comments under these that can't be voted up or down.
For example I go on this link while I'm connected to YouTube:
https://www.youtube.com/watch?v=FSfDzuTLhPU
I see the thumbs up / down for the first 40 comments then the 41st and below have no thumbs up/down anymore.
Why is this?
Best Answer
This is probably due to the comment system overhaul that happened around the end of September 2013.
An NBC News article mentions this:
So with that you'll note that any comment left before the end of 2013 will mostly likely no longer be something you can vote up or down on.