What determines whether a rubygem should be ported or not?

[Matthew Closson]

Greetings!  What determines whether a specific ruby gem should have a
FreeBSD port created for it or not.

I've looked at the list of available packages / ports that start with
rubygem-* and its not obvious to me if its because the gem really required
some platform specific patching to build and install correctly on FreeBSD
or if is another reason or if its just arbitrary that someone decided to
create a port for a specific gem at one point in time.

Thanks for any information on this.

                 -Matthew-