Hi mate, no reason in-particular I just never thought there was a need to as there is nothing in the paper of P/board that the adhesive don't like, it's not touching the gypsom, i'll prime it if it has got dusty but other than that i don't do it...... hope i aint mistaken as i aint going back on all them jobs now now :lol:
It won't be a drastic problem... Ha ha
I just follow Weber's priming for most things 😀