[joekrill]

Because as a developer you can simply run `docker-compose up` and have your development environment working immediately without having to ensure you have all the necessary dependencies installed locally.

And even if you think setting up a "sane development environment" is simple, it gets much more complicated as you add additional languages and versions of those languages, and their underlying frameworks, etc. For example if you look at NodeJS alone: we have things like nvm to switch between Node release versions because you'll often have different projects relying on different versions of Node. Or you could just use Docker and it's baked in, basically.