It doesn't require developers to run ./autogen.sh, or to have autotools installed (in their correct versions).
It doesn't contain obscene amounts of indirection, where the actual libraries live in a hidden directory called .libs (looking at you, libtool).
It doesn't make you write m4, or Makefile.am files with all these magic incantations. It doesn't make you delve into the guts of these crufty systems when things don't work the way you expect.
If you want build systems to satisfy your use cases, publish some doc of best practices and capabilities that all build system interfaces should provide. If I'm convinced I'll be happy to conform to the interface you need. But there is no way you're going to convince me that everyone needs to just keep using autotools (a specific implementation) forever. I hate them.
I mean, by that logic, why are you doing something new like GNU Guix when everybody already knows/uses APT, RPM, BSD ports, etc? "Just learn [them], get over the fact that they contain backwards-compatibility crud (that you can just ignore, or how does it hurt you?), and stop the FUD."
Or maybe it is worth breaking with the past sometimes, when you think you can do better.