Isn't the whole reason why they bought LJ was to get the staff who knew how to make such features?

I'm guessing the reason they bought LJ was a). to get Brad, who had experience making high-traffic hosted sites scale on minimal hardware expenditure, and b). to control the major competitor for their planned new product. Then Brad left as soon as his golden handcuffs unlocked, Vox didn't have the adoption they were hoping for, and they were stuck with a userbase they didn't understand and didn't want, so they sold it off ASAP to somebody who did. :P