I agree. Coding programs for homebrew devs, like GB Studio, have been doing this for the original Gameboy relatively recently, and it seems to be rising in prominence from what I've seen -- it would be so great to have more focus on the GBA as well nowadays. It's clear they agree because of the dev site they run as well. It's appreciated!
I think it must be a mixture of wanting to breathe new life into old hardware you love so much from your past, and also the smaller scale of the creative projects that it allows.. also the sounds, and the visuals (sprites!).. endlessly appealing, isn't it? IMO, this is where projects like GBG have LOTS of appeal and charm (and as they say, limitations can breed creativity), and not only that, this'll later be ported and enhanced on multiple platforms so we get the best of both worlds. So cool