Build tools are complex because builds are complex. Of course, if you create a bespoke tool for your specific use case and then a bunch of other people use it but it doesn't really gain widespread adoption, you can keep stuff simple.
I'm not saying that there's not accidental complexity in current build tools and that a new build tool couldn't strike the balance better, but a rarely used build tool being simple doesn't really say much (and this much is true for almost any kind of software).
I'm not disputing anything you say, but my comment was aimed at explaining why someone who doesn't like dealing with build tools would want to write one.
I don't want to have to defend their choice or explain why build tools are often complex and cumbersome.
I'm not saying that there's not accidental complexity in current build tools and that a new build tool couldn't strike the balance better, but a rarely used build tool being simple doesn't really say much (and this much is true for almost any kind of software).