Keep in mind that there are many points deciding which champion is getting the next VGU.
An example: Visually and gameplaywise, Urgot was the champion with the biggest need of a VGU. But Warwick and Galio still got their VGU before him.
The biggest factor was that they actually need ideas to work with a champion. Do you want them to just slap some random skills together and call that the new Nunu?
I hope you don't, because I surely don't want that to happen. They should have a clear idea of who the champion is, thematically and in gameplay. Creating a new self for Warwick and Galio was easier than for Urgot, so they got reworked first. It took some time to come up with the shotgunknee mechanic, but when they finally figured out in which direction they want to take Urgot, he got slated for his needed VGU.
And I understand that roles are a factor here. Keep in mind that not every player in this game plays every role.
For example: If you don't play jungle at all, it is pretty frustrating to see Riot updating 5 junglers in a row. To keep that frustration at minimum, they try to alternate between the positions as best as possible.
