Why are the GBC gens so ignored?

You can do anything anytime without tools too. I fail to see the point you're trying to make. If people can't change one line of plain text in a file then I don't think we're really gonna miss much from them. I highly doubt that they'd be capable of making anything worth playing with or without tools

The tools are Cygwin, rgbds, and Notepad. Seriously. Anyone who can succesfully use a bunch of ad-hoc tools that make black-box changes to a ROM, let alone understand those changes via hex editing, can get the rgbds assembler to work. And it even has a cutting-edge interface inspired by Google and Cortana, where instead of picking things from long dropdown lists, you type their names instead. Much more user-friendly. ;)

I'll admit that data can be scattered across lots of different files, and it's not always clear if you've updated them all. But the community is quite helpful with that: Pia Carrot wrote an intro guide to common tasks, and Skeetendo is focused on Gen 2 hacking (I've written up how to add new moves, maps, and NPCs).

(Another advantage of assembly: it's all text. If you don't already have a pretty thorough understanding of ARM machine code, you'll depend on pre-made tools and patches for editing Gen 3 games, without really understanding how they do what they do. But with assembly code, you can learn by reading it, and add completely original features on your own.)