Why must summer squash be harvested soon after its fruits form?

Summer squash, which belongs to the order Cucurbitales, must be harvested shortly after the fruits form to ensure they are consumed while they are still immature.12

These fruits develop very rapidly, and harvesting them early—typically a few days after formation—is necessary to prevent the seeds and rinds from hardening. Because summer squash is cultivated specifically to be eaten while the rind is still tender and edible, allowing the fruit to mature fully would result in a tougher, less desirable texture. If left on the plant to grow larger and reach full maturity, the fruit becomes a marrow, which has a significantly harder rind.132