A couple of weekends ago, together with a small group of like-minded idiot mates, I took part in the Paris - Roubaix sportive, the day before the pros got their chance. I can assure you that over the route we/all those taking part left quite a lot of litter in our wake like bottles, gel wrappers, empty chip wrappers etc.
Yet when we returned at 5.30am the following day to secure our vantage point to see the pros do it properly, all the litter had gone.
Immediately after the pro race a couple of course trucks with litter pickers followed and within 30 minutes of the riders passing by, no evidence of their presence was left. Also spectators help with clearing up because we value these races and don't want locals objecting that they're ruining their, often lovely, rural areas. It's the same with the TDF.
Go round the London marathon route an hour or so after the last runner has passed and you won't find any litter either.
So it can be done, it's just that the Stafford organisers can't be arsed.