Intel and AMD are market leaders in raw price/performance. They drop mad money on custom designs at cutting-edge nodes to do it, too. The Cavium chips might be custom but probably standard cell. Cost way less. Further, you get 16 RISC cores with no x86 baggage, they run Linux, PCI form factor, and low power. Onboard are usually accelerators for TCP/IP, compression, encryption, and so on that run in Gbps that your processor cores don't have to handle. The CPU cores themselves run pretty fast.
The hybrid seemed like one of the best designs. Probably why AMD started copying it with their semi-custom business followed by Intel. But those are still full-on x86 processors with all kinds of circuits you probably don't need plus maybe some backdoors for AMT, etc. Cavium's design is much more interesting and maybe safer. I've mainly encouraged people to clone it with RISC-V cores rather than straight-up buy them. ;)
The newer ones are pretty impressive in performance and accelerators, though:
https://www.cavium.com/OCTEON-III_CN7XXX.html