My main reason would be not having to set up my computer for development. When you're new to an ecosystem it can be super painful to get set up.

Example: I use Python a lot, but had never used it with MySQL until yesterday. I had MAMP installed and I just wanted a Python package to run queries. I tried to install MySQL-Python, but it couldn't find mysql_config. So I find it and update my PATH. Then it can't find some files. I google it and it turns out MAMP MySQL doesn't include some parts and I need to install another version of MySQL to make it work. It works now, but the MySQL Workbench export/import feature isn't happy with the MySQL version number.

Especially since many open source projects are compiled from source and have many dependencies I'd love an environment that just works.