I believe why they are not more popular is for two reasons. Firstly, to use a 'Plummerism', there would be a fair bit of litter wastage, heavy, strong pups and back say, in the 60's and 70's this would have put a lot of lads off breeding a litter and the knock on effect is with us today. Secondly, Labs have a reputation of being late starters (which may be completely untrue, i aint got a clue as i've never owned a Lab!) And like GSD crosses could put lurcher breeders off...?
The dog Kevj mentions was owned by the bloke who wrote in EDRD years ago under the name Greylab. The dog was a very