SiFive have apparently been shopping themselves around for a while. But they've been around for a long time, taken loads of investment, had a huge number of employees at one point (not now), and don't have very competitive products. My speculation is they're just not a very attractive acquisition with a complex ownership structure, and are demanding too much money to compensate their earlier investors.

Might be worth more than Qualcomm is willing to spend and/or introduce antitrust concerns. This feels like a hedging of bets, no need for Qualcomm to buy the biggest name in the RISC-V space.

SiFive have had a very long time to create competitive CPUs and they haven't really managed it. I dunno what's going on there but I'm not sure I'd buy them either.