Potrebbe essere mancanza di acqua.

Anche mancanza di cibo nel terreno. Le zucche sono dei mangioni grossolani.

Potresti anche sfoltire le tue viti. Diciamo tre viti alla radice originale.

First, there are seperate male and female flowers. Male flowers have just a thin stem below the blossom, whereas the females have a small lump that looks a bit like a mini fruit (the future pumpkin) - if it's the males that are falling off, it's normal - if it's the females, they're not being pollinated and doing some hand pollinating with a soft bristle brush may help. The male flowers will last a few days, the females usually just a day or two, and are best pollinated the morning they first become fully open. Unfortunately, sometimes when the females are just opening, there's no males out! This is more likely with just one plant, vs a pumpkin patch with several plants.
Are you encouraging pollinators like bees and butterflies? That makes a big difference. One other possibility, given you mention lush growth, is too much nitrogen in the soil, which is great for vegetation but not flowering and fruiting.