This is all compounded by the fact that there is no app bundle. Mac OS X has the bundle and a terrific way to install it: Drag and drop it into the Applications folder, just like we did in the days of the Mac Classic and MacPaint. It hasn't changed. (Well, it did for a while, but thankfully they went back.)
If you say, "Well, that means you end up installing 5 different versions of the same library on the same system" - Who cares? Disk space isn't a priority any more, and from a developer standpoint it makes a lot more sense to target a dependency whose version number I know, instead of a dependency whose version only the package maintainers know for sure. I don't want to be forced to target v1.3 of a library if it's only been tested (by me) on v1.2. It makes for much better application stability for the developer to be in control of dependencies and not these package maintainers.
I want to ship a self-contained bundle of awesomeness, not a dysfunctional shard among ten thousand other shards.