I don’t think it’s just the weather though that will have a large effect.
Spent all our money on summer holidays etc .. now need to work a bit more to make it up again in time for Xmas, stay in and save just biking and using consumables costs money – though pittance I know, but it is that rough middle of the month spell where cash flow for the next two weeks start to rear it’s ugly head (not me – I’m paid weekly)
Everyone back to work proper, i.e. less taking time off.
Just darker in the mornings and evenings creates shorter days to squeeze the ‘same stuff’ into for those that don’t do night riding.