As to why being unhappy is probably not because it haven't been proof tested. I get your sentiment but feel the remark is out of place. I thought the rationale for picking other tools was straightforward and motivated.
Though the simplicity of make has been lost and I'm not sure the overhead is worth it. I wouldn't want to be the one introducing taskenv, direnv and derenv to a project.
But it was; one of his arguments. Yes, he opens with the argument that he was unhappy with the Make for years, but he later clarifies why:
> I am still stuck with a tool that (according to Wikipedia) has been written 47 years ago.
You probably haven't read his article to the end? Those were his words I copy-pasted from the blog. So one of the reasons he is unhappy is because Make is 47 years old. For some reason, it stopped to be good enough 20 years ago, according to his opinion.
I can give him that we can always have a better tool, but it is a tautology. Unfortunately, his offered alternative is not better IMO.