Comment by grapheneos

Fairphone 5 and earlier also have end-of-life Linux kernel branches without security support. Fairphone's more recent devices are headed to the same situation. In practice, the same thing happens with other components beyond the Linux kernel.

Fairphones have 1-2 months of delay for partial security backports to older releases from the beginning and much longer delays for full updates. Android 17 is required for full Android security updates. Only a subset of patches are backported to older versions and that subset is decreasing.

Android 17 is also required for the latest and greatest privacy/security protections which are not backported. There have been massive privacy and security improvements in each yearly Android release.