Speculation, but I think it will come down to space and if the queue is able to handle a larger crowd. I know it isn't Disney, but at Universal the Jimmy Fallon ride has very little queue space and it is a slow loading/low capacity ride so they do virtual queue even though the ride isn't very popular. On the other hand, MMRR has a lot of room to accommodate an overflow queue so no VQ. Also at Universal, they do VQ on Hagrid's so as to not block the virtual asthetics of Hogsmeade, which I have a sneaking suspicion is also why they do it on ROTR (along with the frequent breakdowns due to the advanced ride system).