Pumpkin problem

[Doive]

I've grown a variety called 'Big Max' this year, in an attempt to produce a decent sized pumpkin. The plants themselves have been extremely vigorous, long trailing sinewy vines that scramble and hang on to everything. However, every fruit that has set, has grown to the size of a ping pong ball, turned brown and dropped off - with the exception of a single fruit, that is now being gently cared for and fussed over.

The plants are regularly and well watered, morning and evening, and fed a tomato feed once a week, as per the tomatoes. Any suggestions why it didn't produce more fruit? It's in a polytunnel that is well ventilated. I'm wondering if it's been too hot?

[Snadger]

Its more likely to gain a decent size if its the only one. The loss of the others is a pollination issue. We did have a cold spell and there ARE less bees flying around to pollinate. At the time the female flowers were open perhaps there were no male flowers to be able to pollinate them?
I always hand pollinate pumpkins and like you I have one large one on the plant, but that was purposeful.

Maybe these pumpkins have ben bred through selective breeding to be frugal with how many pumpkins grow, to aid the size of the few that do grow?