The reasons behind this could be:-
The papaya seeds were not planted properly i.e. they were planted too close to each other.
Some papaya seeds received proper nutrition while the others didn't
Some papaya seeds were planted in a corner and they did not receive sunlight for photosynthesis.
I hope this helps you and pls give me the best answer ☺™.
When all of them were thrown together, they will all land in the same place. And due to less space they will compete with each other for food, water ,etc. During this competition, the weak one's die and the strong one's stay.