Window gaskets shrink for a variety of reasons, but the most common cause is exposure to extreme temperatures. If your windows are exposed to direct sunlight or drafts from outside, the gaskets can become damaged and shrink. Additionally, if you live in an area with high humidity, the gaskets can absorb moisture and swell, causing them to shrink when they dry out. There are a few things you can do to prevent your window gaskets from shrinking. First, try to keep your windows covered or shielded from direct sunlight and drafts. You can also use a dehumidifier in your home to help reduce the amount of moisture in the air. If your gaskets have already shrunk, you can try to stretch them back into place with your hands. If this doesn't work, you can purchase new gaskets from a hardware store.