It's a big plus if you want to write code for it in something like Rust. LLVM support for the architecture they used on their older chips (xtensa) for a very long time required compiling a fork of LLVM and rustc in order to target the chips. It may still, I didn't keep up with the effort to upstream that target. RISC-V is an open architecture that has a lot of people excited so compiler support for it is very good. Though as far as why Espressif is using it, it feels likely they would use it because it means they don't have to pay anyone any royalties for the ISA.