Question

Why don't all the seeds produce by a plant grow into new plants

Answer 1

The process by which a seed grows into a new plant is called germination. ... During the early stages the seeds will get food from the cotyledons. The seed coat will break and a new plant will emerge out of the seed. When the plant will develop a root system it will absorb water and nutrients from the soil.
If these things are not available the plants don't grow.