Some possible reasons:Reggie wanted to (or felt like he should) have a clean slate for the look and feel as ITT rebrands as t.m.o vBulletin has been upgraded. The theme may, indeed, have been incompatible. vBulletin's themeing isn't as good we think, and there were structural changes to the PHP pages required to get the look & feel working. The old theme just wouldn't work anymore. The old theme would've inherited some elements (say, a header) from the new theme and looked crap. Reggie didn't want to deliver (in his eyes) crap.