How Do Shows Determine How Many People to Credit in Each Episode?

This is something I've always wondered.

One of my favorite shows, as you know all know, is The Amanda Show, especially the end credits because of the amazing music. However, sometimes I noticed not all credits were included and sometimes they were -- they could be all credits and have a long list, partly cut out, or really short. For example, Production Designer and Lighting Designer wouldn't be in the really short ones.

Compare these two videos:

Skip to 4:50 here:

Skip to 4:45 here: