Because the ISA that a modern microprocessor is engineered to execute is different from the Micro-ops execution engine/Other(The Actual Hardware) that's a custom design that's the IP of the creator. And so Qualcomm wants that RISC-V running CPU core design IP that belongs to Ventana Micro Systems and the ISA on modern microprocessors is just a set of execution rules that the actual hardware(Micro-Ops execution engine and associated cache subsystems/other parts of the hardware and that IP that belongs to Ventana!) is engineered to execute.
Qualcomm also wants the RISC-V engineers and their Knowledge and the Software Ecosystem and SDKs/Tools that Ventana has developed over the years to create CPU cores that execute that RISC-V ISA. And that includes all the design Verification tools/EDA tools that Ventana developed for their specific CPU core designs and all that non hardware stuff that takes a larger investment in dollars than just the hardware's development alone costs!
So the RISC-V ISA is Royalty free but not anyone's actual RISV-V ISA executing CPU core designs that cost millions to create and are the proprietary part of the Acquisition that Qualcomm is after. I'd imagine that Qualcomm's Nuvia engineers could more rapidly swap out the ARM ISA Instruction Decoders on any Oyron cores with some RISC-V Decoders and use most of the same Oryon Micro-op engine design that's native to the current Oryan generation cores but maybe Ventana's micro-op execution engine has something that's valuable to Qualcomm as well.
And so ISAs on modern microprocessors are abstracted away at the actual hardware level by the Micro-ops execution engine desogns that are proprietary to the ones that created them. And the reason that many license from ARM holdings is not just the ISA but the software/OS/Drover ecosystem that's built up over the decades for the ARM ISA ecosystem and that costs many times more than the hardware's costs to develop and maintain over the years. And so the ARM OS/Software/API and driver ecosystem is decades more mature than the RISC-V OS/Software/API and driver ecosystem, and that took years and 100s of billions in investments to get ARM where it is today!
But since RISC-V is royalty free there are hundreds of companies using RISC-V, including Nvidia for it's FALCON(FAst Logic CONtrollers) that are used all over Nvidia's GPUs and other accelerators. And with RISC-V one is free to implement only a subset of the RISC-V ISA or create custom RISC-V ISA extensions unlike ARM holdings where licensees have to implement the entire ARM Licensed ISA regardless of if all the instructions are needed for the task and no ISA extensions allowed.
So maybe Qualcomm is interested in the micro-controller market that's lower margin and that makes RISC-V's Royally Free more attractive! Or Qualcomm, like Nvidia, wants to develop some RISC-V Micro-Controllers for it's own in-house needs and not have to pay for ARM Holdings ISA based Micro-Controller designs. Look at Nvidia's dozens of on GPU die Controllers(Encoder/Decoder Logic,Etc) and because that's Nvidia FALCON RISC-V based that's quite a bit of savings in Royalty Payments and CPU core design payments to ARM Holdings or anyone else because FALCON is Nvidia's In-House IP and that RISC-V ISA is free to use for Nvidia or others to save billions that way.