I think there are several reasons and my understanding is probably mostly wrong. First, the original port was using Uboot and then the focused shifted to uefi.

I think there are several reasons and my understanding is probably mostly wrong. First, the original port was using Uboot and then the focused shifted to uefi. Around the same time efforts shifted from a port to raspberry pi to use fdt and support for arbitrary boards. This should give a more flexible solution with the downside being less focused development. The risc-v port probably benefited from the work stated above and stayed focused on a particular board.