Well the best reason is that it seems you might just be alone in that room soon and be charged with having to turn the lights out when you leave
Well to be serious I also had those feelings but now down the line it was the best move for the forum all round. We have better support really nice software and my members are very happy all round. So just for that it was worth the effort to move.
1) vB3 - Dead.
2) vB4 - For the most part, dead. No development, most likely security patches only.
3) vB5 - I don't need to tell you about that.
4) IB is now owned by the same people that own GoDaddy.
5) https://snogssite.com/threads/notice-premium-vbulletin-add-ons-end-of-life.625/#post-8712 (and they've lost another 300 users since that post, or another 10% of their users since June 18th)
XF - Full support and constantly under development.
I used to use vB back in the day. I just found it way to complicated to use as the AdminCP wasn't the most well laid out in the world. After vB4 I just can't see using it anymore as vB5 is a joke. xF just keeps gaining more and more ground in the forum market. It's fast and easy to use. All around better software and it's brought to you by the 2 guys that made vB3 as good as it was.
Yes the redirects for the DBSEO links are important, that's what worries me the most.
I was quoted $200 for someone from Xenforo to do all the above which I thought was a lot...