It's a known problem that the base system is unable to fetch an up-to-date ports tree:
PR 254856
Nobody seems to be in a hurry to do anything about it.
That's not true, probably someone should close this PR (or maybe it's left open because somehow supporting GIT in base is wanted for the future). Anyways, the portsnap backend works with GIT for quite a while now.
Portsnap snapshots were never perfectly "up to date", but pretty close, this didn't change. The idea to remove portsnap (for many reasons, the most important one being it never supported the "quarterly" ports) exists, but that's kind of unrelated. As of 13, portsnap is still supported.
Next, delete the entire ports tree and get a new one with git.
Well, if you don't want to actually use GIT (there are reasons you might want to), this step is unnecessary. Just continue to use portsnap if you're fine with it.
edit: claims that you
need git (or gitup) are from the short time after 13.0-RELEASE when the portsnap backend wasn't adapted to GIT yet. Back then, they were true. And just for completeness, it's not related to 13 at all, the timing was just coincidence – ports are independent from base system releases, so all this applied to users of 11 or 12 as well.
The situation for getting/updating your ports tree ist mostly the same as it was with SVN: You still either just use portsnap, or you get it directly from the source repository. The only difference is that for the latter option, there's
svnlite
in base, while there is no such tool for GIT. It doesn't matter as long as you use portsnap. Even if portsnap would be gone in 14, I personally don't think GIT support in base is needed, as you can always install an initial ports tree from your installation media and build/install git from there. But I guess that's still an open discussion, one possible solution could also be to e.g. include gitup in base.