Patty Pan squashes

About 5 weeks ago I sowed individual seeds in seed compost in small pots and put in my mini greenhouse, keeping well watered and ventilating on hot days. There are 16 pots from 2 different seed packets, a white variety and a green/yellow mixture. Well, all I have is one plant which came through about 10 days ago. Why do you think the others haven't germinated? I have poked around in a few pots and the seeds are still there so not been eaten, and I have used organic slug pellets.
I usually put excess plants on Freegle - I don't think it will happen this year!