As a matter of fact we can control the eggspawnspeed. It's not the ai or anything, it's ballancing that keeps the spawnrate down. Infestors aren't supposed to be a one man army and I do believe that they are strong enough at the moment.
Btw., randomly spawning eggs wouldnt be nice, infestors would waste all their eggs on the way to the fight O.o and/or a lot of infested terrans would never reach their opponents.
I dunno, I get the feeling this sounds a bit aggressive.. it's not supposed to... feel free to add more arguments!