Fairphones are designed and made for Fairphone by T2Mobile which is a Chinese ODM. Fairphones have very poor updates and security. Those devices are incredibly far from meeting the requirements for GrapheneOS and cannot be supported. Fairphones aren't European phones but rather Chinese designed and made devices sold by a European brand. T2Mobile not only designs the hardware but also builds and signs the firmware. Fairphone does very limited engineering and mainly combines AOSP, Google Mobile Services and the firmware/drivers from T2Mobile to make the stock OS. They're not in a position to meet our requirements. T2Mobile doesn't provide good security in practice and would need to greatly improve. Trying to get an ODM to improve security is only realistic with a security-focused organization as their direct customer and Fairphone definitely isn't.

And there couldn't be reasons to buy a phone that includes hardware made in China which thus runs firmware components made in China. So long as you don't have to work in a cobalt mine yourself, who cares about non-security benefits right?