Because it's made of extruded silicone. It stays nice and soft in the coldest weather and does not dry out and crack up. It's a utilitarian weatherstrip. The FLAP model covers a wider gap and offers a more forgiving installation.
All models use extruded silicone for the gasket material.
We call it the World's Best weatherstrip because we think it is. This model comes in White or Brown. The gasket material is silicone and the stabilizer is weather resistant plastic. If you don't agree that this is the best weatherstrip you've ever used we'll give you your money back. How to install door weatherstrip.