A lot of things collapse when the weather changes. Things like apples need a period of cold weather over winter. Often multiple things are synchronised, like the flowering and growth of particular plants and insects and animals that are part of cycle of polination, or predators that eat pests etc. Even very small changes in climate can have major effects on the way everything works together.

A lot of plants literally require a cold period to fruit (berries, etc). Constantly warm weather makes a lot of plants lose their shit, it's like foregoing sleep. You think you're good at first, then the wheels come off.