First, the whole point of RISC-V is that if you use it to create new processors, you do not have to pay any licensing fees to anyone. If you want to use the ARM or x86 or AMD64 instruction set in a new processor, you will have to pay a license fee to the owners of these instruction set (Arm, Intel or AMD respectively). Due to the cross-licensing agreement that Intel and AMD have with each other to license each others instruction set (x86 and AMD64), it has negligible financial impact on their profit margins.
Second, Intel and AMD's x86 and AMD64 are the dominant platform on server and desktop market today. ARM instruction set architecture (ISA) dominates the mobile platform and is only now competing with Intel and AMD on the desktop and server market. If Intel or AMD drop support for x86 and AMD64, and migrate to ARM, it will make ARM the dominant ISA on which all IoT, mobile, desktop and server softwares run. This is obviously not in Intel or AMD's interest. Migrating to RISC-V would mean they have to help promote a completely new ISA and help developers migrate their software to it. Doing so will also kill the x86 and AMD64 platform.
So unless RISC-V ISA actually offers some real technical advantage (like drastically lowering the power requirement and boosting computing performance) it really makes no sense for Intel and AMD to shift to it.
Note that the news here is not that Intel and SiFive have built a RISC-V chip but how SiFive (who have ventured into making RISC-V chips) has partnered with Intel Foundry Service to make the chips in Intel's fab. This is Intel diversifying to also make chips for others in its foundry like, Samsung and TSMC already do.
"SiFive (who have ventured into making RISC-V chips)"
SiFive don't make RISC-V chips, except in small volumes as a demonstration. Their business is licensing CPU cores to companies that do make chips.
"Horse Creek", as its naming style suggests, is an Intel product that uses licensed SiFive CPU cores. SiFive will use the chip to make high priced dev boards. We don't know yet who else will use it.
The apparent success of the project is likely to get other SiFive customers to, as you say, use Intel Foundry Services instead of the traditional TSMC or Samsung.
I don't know whether Intel is designing high performance RISC-V cores of their own. It's not unlikely. But there are also others announced to be providing cores to Intel Foundry Services including Rivos who are developing an M1-class RISC-V core (they have a number of Apple's core designers, including some of the founders of PA Semi who Apple bought to establish their CPU design team in the first place)
Second, Intel and AMD's x86 and AMD64 are the dominant platform on server and desktop market today. ARM instruction set architecture (ISA) dominates the mobile platform and is only now competing with Intel and AMD on the desktop and server market. If Intel or AMD drop support for x86 and AMD64, and migrate to ARM, it will make ARM the dominant ISA on which all IoT, mobile, desktop and server softwares run. This is obviously not in Intel or AMD's interest. Migrating to RISC-V would mean they have to help promote a completely new ISA and help developers migrate their software to it. Doing so will also kill the x86 and AMD64 platform.
So unless RISC-V ISA actually offers some real technical advantage (like drastically lowering the power requirement and boosting computing performance) it really makes no sense for Intel and AMD to shift to it.
Note that the news here is not that Intel and SiFive have built a RISC-V chip but how SiFive (who have ventured into making RISC-V chips) has partnered with Intel Foundry Service to make the chips in Intel's fab. This is Intel diversifying to also make chips for others in its foundry like, Samsung and TSMC already do.