Because they're not funny or enlightening. It's impossible to put anything of meaning into a six second clip. There's no background, no resolution, only the bit of action without any context.
I always find it interesting how deaf people are so free online without barriers... Id love to have a deaf friend to ask questions about their experiences and learn bsl from :D i hope this doesn't sound patronising, i mean it sincerely
To learn about deaf culture, I highly suggest the TV series Switched at Birth.
Also, although not the same thing as being deaf, you might enjoy this Youtube channel:
https://www.youtube.com/user/TommyEdisonXP
It's about a blind man who answer questions about being blind.
What obscuredangel says, Switched at Birth is a great TV show that while you won't be a master in the deaf culture it gives you a perspective of how life goes around deaf people and its community. It's also cool how other hearing people are showing interest in learning sign language! :D
Also, although not the same thing as being deaf, you might enjoy this Youtube channel:
https://www.youtube.com/user/TommyEdisonXP
It's about a blind man who answer questions about being blind.