It comes down to the lack of resources for a platform that is rarely used for new installs. The number of machines running 32-bit FreeBSD/i386 11.x and 12.x are the same as other Tier 2 platforms, such as ARM, RISC-V, PowerPC and MIPS. AMD64 CPUs have been available since 2003.
FreeBSD are not responsible for maintaining legacy platforms, it is the job of the administrators and users to keep both their hardware and software up-to-date and maintained.