The market is still only a fraction of the size of vBulletin's.
In addition, our forays into xF were met with a hostile reception from vocal sections of the community, including attacks on us from other mod makers at xF. We got more negative comments and attacks in 2 months from the XF community than we had in two years from the vB community - despite the vB community being hundreds of times larger.
Our coders have said they would prefer to not deal with that hassle. The two factors combined make it unlikely we will make a sustained push into xF any time soon.