Except that those "more current" packages are often months behind the most current versions as well.
That so many PPAs exist for so many packages should be a clue of that.
Up to 6 months can pass (new release) for things like the Firefox release that too significant of a change (not just bugfixes, but a new version) to backport into the previously release version of Ubuntu. Bugfixes and minor revisions make it fine. But there were a lot of Ubuntu people adding in the firefox PPA to get the new version as soon as it came out.
Other distros, such as Fedora (which I used to use until recently) do the same thing.
But this is "months", not "years". Big difference.