It seems that all but the default system theme have been disabled for users. Unfortunately, this move was not added to the change log, so hopefully this means the change was intended to be temporary.
It would be a nuisance to have too many themes because they would need to be maintained. We do quite a bit of behind-the-scenes edits to the themes, so keeping many themes over time would create a time-consuming maintenance game. Carpetsmoker points out that the default theme at BSDForums.org never seemed to bother anyone, but then again, Dinesh's inactivity made certain that complaints would fall on deaf ears.
Ultimately, our only choice of themes are here:
vBulletin.org. Yes, there are many more themes for vBulletin, many of them nice-looking, but I highly doubt any of them run with 3.7.0, which is the five-day-old version of vBulletin with GUI abilities incompatible with themes made for any previous versions.
Finally, vermaden has been away for nearly a week now (He should be back Monday), so we do not know what his input on the matter is. However, it is our hope to eventually create a custom DaemonForums theme that will become the default theme.