@Rodrigo Campos
In my case the U-Boot side is not just a generic version choice. That baseline carries the board-specific path I tested: the zero2w-based defconfig, mmc0 broken-CD handling, H616 EMAC1/RMII support, I2C3 enablement, the LAN preinit step, and the extra EMAC-related clock/register writes. Since the kernel LAN attach depends on the board already being prepared by U-Boot, I preferred to keep the bootloader side conservative.
So the short answer is: it is pinned because it is the validated baseline, not because I know of a hard conflict with every newer release.