Well if you mean those who mock him .. well it's because it's disrespectfull and we don't even accept it for Jesus
we don't know how he looks so we don't go drawing about his shape and all that .. it's like if you want to draw god?
you don't know how he looks and you just don't draw him
(P.S i'm not saying he's like god .. just giving an example)
that's what i think it least