Is it? Anyhow, it does not mean that it is illegal, which was the original question. I guess most ToS are not enforceable in practice. The worst that may happen is that you "lose the warranty" of your macOS install and you cannot ask Apple for support. No big deal.
Just because software is made available using a public web server does not mean that you are free to use it as you please. It's distributed along with a ToS agreement that governs its use.
Bringing in words like "illegal" can be fraught because I don't think we've seen a court case (in the US at least) about exactly how binding a "click-wrap" agreement actually is, but there's no question that projects like the one linked upthread violate the terms of the software license.
