It's extensible, so they could in theory introduce something to the ISA which would give them a competitive advantage, maybe even a publicly available extension that their competitors have simply left out, e.g. one of the crypto extensions.
There's also the benefit of being more flexible with teams who work on your SoC. With RISC-V, everyone has an ISA license, so they can contract, team-up, collaborate, or do basically anything they want, in order to work on their chips.
This also means that acquisitions are a much richer market than they are with other ISAs; in part because you don't have to justify the cost in time, money, and uncertainty of licensing or planning to license ARM.
There's also the benefit of being more flexible with teams who work on your SoC. With RISC-V, everyone has an ISA license, so they can contract, team-up, collaborate, or do basically anything they want, in order to work on their chips.
This also means that acquisitions are a much richer market than they are with other ISAs; in part because you don't have to justify the cost in time, money, and uncertainty of licensing or planning to license ARM.