Bitbake is a bit further than 'recursive makefile', it's much more along the lines of a package manager like nix or portage (though it's less well designed in most aspects, the build file syntax is insane and debugging it is a nightmare. I think it's grown the necessary features instead of stepping back and understanding the problem). And it's important to realise it's mostly focused on building packages like a linux distribution, even if the systems are rarely managed by installing/uninstalling packages. This is where the whole idea of taking an upstream tar or repo and patching it together comes from, and it makes perfect sense when 90% of your workflow is 'take someone else's code and modify it slightly to integrate into your system', especially when that code gets updated (it's still not painless, but you have some hope of doing it). When you're google and can afford to rewrite huge parts of the system and have no need for compatibility then you can make a more nicely integrated system, but most embedded applications cannot afford this.