I buy a couple of tins of paint and some wood panels to do some diy in my living room. I don't expect the paint manufacturer to give me the ingredients and procedure to recreate the paint from scratch, and I don't expect the wood manufacturer to tell me how to grow my own trees. Yet I spend a bit of money to buy the items to perform diy.
It's the same here. Minicircuits are providing a kit, which can be assembled together yourself, if you pay for it. Why does it need to be open source when they aren't calling it open source? They are providing a kit for a niche market, which the vast majority of electronic hobbyists are not included. This isn't uncommon. Terasic sell dev kits for thousands of dollars. So do many other manufacturers: microchip, linear, etc. Most are far overpriced and are not intended for hobbyists.
This is firmly aimed at the university market, for the use of (not purchase!) students and possibly researchers. It is not very practical, but it is not intended to be a great VNA, its a relatively cheap, complete kit for universities to buy. Universities by and large don't wince at such price tags, as they will have budgets to spend and the real deal is the time it saves in preparing work for students. If I was a prof working on some interesting labs for my students, buy several of these kits might be quite appealing as I don't have to waste time researching all the bits and ensuring they will work myself. This is often the primary selling point, and where it is actually "useful", though I do sometimes wish things weren't quite so expensive.
Sometimes the bean counters are wrong, but if the product is a flop for its chosen target market then we might see it withdrawn