(1) No real space up front to stow all nourishment that pilots require (A lot!)
(2) Would hardly be safe to be pouring and preparing drinks in the flight deck
(3) Would have to employ another cabin crew member to be up front to do (2)
(4) No toilet on flight deck, except on some widebodies, so flight crew have to move in and out anyway
(5) Too much hassle for no gain