At the moment their current OS is backwards compatible with the 32-bit Model B+ they released back around 2014, so only one distro to maintain and one set of kernel modules etc. I can imagine they probably have a very close relationship with Broadcom at this point too…
It’s slightly disappointing, but it’s still very, very early days for RISC-V, some things just aren’t there yet like the value for money, performance per watt, and support for various hardware features. In a few years though things will look very different…