MacPorts is full of useless junk. MacPorts will install a new sandboxed python, ruby, perl, etc when just want to get wget (the built in versions are fine!). The libraries are all broken out where brew keeps them simple and a lot of the packages are old silly packages that no one on the Mac really cares about (every single GNOME library for example).
brew isn't just moving forward quickly, it has really just out right replaced MacPorts and anyone still using MacPorts is living in 2007.
MacPorts does not use system libraries for good reasons:
"There are several reasons why MacPorts uses its own libraries. It makes ports more consistent across different versions of Mac OS X. For example, if we can rely on openssl 1.0.0 from MacPorts, we don't have to test every port that needs ssl for every available openssl installation. Apple's software tends to break from time to time (e.g. openssl refuses to build with an old zlib, but for awhile Apple shipped the old headers of the vulnerable zlib version). Even if Apple's versions aren't broken, they're rarely up-to-date. Apple has a habit of not updating the libraries in Mac OS X until absolutely necessitated by a security vulnerability." [1]
But yes, arguably, `brew` is moving forward very quickly.