You're a user - I'm purely referring to contributors.
It's clearly gained popularity for good reasons - it's an API that is very user-oriented, with reasonably good UX for most people. The downsides are mainly related to issues users don't see (i.e. security).
Homebrew adds a location to your $PATH that is writable by unprivileged users. This means any non-root process has privileges to mask any binary on your system. They do this in the name of "convenience" - so that the Homebrew process can install apps without the user entering their password every time.
I install it on my Linux devices too. It allows me to easily install up-to-date versions of just about any software I care about.