I'm probably in the minority here but I would never run this if given the option. Most of the stuff in here has nothing to do with development as is just personal preference. Like what are you hoping to accomplish by dropping `ag` on my PATH? It's just not a tool I use.
The stuff that's specific to development -- go, node, npm, etc. -- sure that makes sense, but installing that stuff via brew is vastly inferior to versioning it as a dependency within your build system. And I'm not saying you have to use bazel or something. Pin your versions, install them by script in the context of your build tools and leave it at that.
I'd reckon the reason you don't see this sort of thing often is because it's not actually useful or necessary. I'd rather follow steps in a document somewhere so I can ignore the steps I don't care about and share steps I find useful.
It's like showing up to a job and them saying "hey we've preconfigured emacs for you."
I'm a professional and take pride in knowing my tools. I can set up my development environment myself. I use Nix where possible and tend to avoid homebrew. Half of these things I have in my dotfiles or nix configs already, as do most of my peers.
I'm sure others will find this useful, and there's certainly nothing harmful about this, but it's certainly not for me, and I'm certain there's a better way to go about handling all these things.