Isn't it more that it's just cheaper? If Council staff count overnight they get paid for it and paid at a higher rate of pay. If they count during their normal working hours however then it's just their normal pay?
Also general exhaustion - a lot of the count staff have been working throughout the day already!
Where I am, turnout was definitely up and there were certainly people who don't vote or indeed very rarely vote who seemed to come to vote quite early on in the day before the more "traditional" voters. I'd suggest many of the people who ticked the turnout up, almost certainly were heavily Reform. Also I challenge how well informed they are - I certainly saw "Starmer Out" stickers around... but like it or not they have a right to vote, even if they are completely detached from local issues.