SiFive is in the business of selling IP cores and back-end implementation services. The gold standard for IP core validation is "silicon proven" i.e. that it's not just a nice theoretical design on paper, but someone has actually turned it into a physical chip and tested the real life performance.

Lots of people will try to sell you their designs and services. Picking the wrong ones can waste millions of dollars and months/years of time.

The money spent on this a prototype buys SiFive credibility for both aspects of their business (assuming the chip works) - "we were able to do this for ourselves, so you know we'll be able to do it for you".

So it's not a waste, it's a marketing expense, and a necessary one.

The article mentions that is is from the OpenFive division of SiFive. OpenFive used to be Open Silicon and their business model was working with other companies to take their Verilog RTL and do all of the physical design (synthesis to logic gates, place and route of the standard cells, timing analysis, test vector generation) and then work with the foundries to deliver all of the data for manufacturing.

Since Open Silicon is now OpenFive and part of SiFive they literally have all this experience in house and don't need to depend on another company between them and TSMC.

https://en.wikipedia.org/wiki/Open-Silicon