Fairphone doesn't design or make their smartphones. The devices are designed and made by a large ODM. It's entirely feasible to use a modern SoC with current generation security features and provide proper updates. Their ODM isn't doing it to cut costs.

Fairphone quickly stops providing Linux kernel updates and has months of delay for Android userspace backports along with driver/firmware backports. The delay for yearly updates typically starts at a year and gets longer as devices get older and they've always skipped the quarterly updates.

Using a modern SoC, properly configuring it, using proper signing keys (Fairphone has repeatedly used publicly available sample private keys) and providing proper updates is most of what's needed to meet the requirements. That's entirely doable by the few OEMs designing their devices in-house such as Motorola Mobility. Samsung and Google along with many of the ODMs making devices for Nothing, Fairphone, etc.

https://discuss.grapheneos.org/d/24134-devices-lacking-stand...