Why would someone use OpenSPARC rather than riscv? Seems like the Linux distros have some a-tier support for riscv64, or will soon. Debian supports SPARC right?

Why would someone use OpenSPARC rather than riscv? Seems like the Linux distros have some a-tier support for riscv64, or will soon. Debian supports SPARC right? Anyone else? That's not even getting into upstream testing. I imagine there is more development attention to riscv tooling e.g. GCC, llvm, glibc, musl, util-linux, et cetera.