Timeframe + team probs
There's too many 'kids' on that bus and they've got no distinguishing traits at all. What a boring group of young people.
So I've been thinking about the era these movies are supposed to be set in, and I think it's purposely ambiguous. They want to keep the technical simplicity of older vehicles, no ubiquitous cellphones, costuming and hairstyles that could be from 1961 or 2011. And I may be completely wrong but I think the idea is to be able to make sequels and expand the story without triggering nerdrage online about retcon and chronological jibber-jabber.