I am prepared to get flamed for this but I think, working in the industry, there are a lot of misconceptions about how courier services work.
Yeah, I kind of agree with this too. I work in retail and we work with DPD. I know most of our drivers well - they deliver to us 5 days a week so we know each other's name and have a quick chat most days.
They're always stressed as anything. The expectations on them are ridiculous and they're expected to work until they've finished every delivery, even if that means a 12+ hour day driving around. They don't get paid particularly well either.
Recently we've had a lot of newbies being trained alongside our older drivers, but there's no extra time built into the day to train them properly. It slows them down (as it does when you're being shadowed all day) but they're still expected to do their job in time. I just don't see how it's possible.
Add into that normal things that delay drivers - traffic, school holidays, bad weather, accidents, vehicle breakdowns, roadworks and you can see how it's just impossible to get everyone's delivery there on time. They have vans full of goods, some which will be on a pre-12pm drop-off, some next day, some that need to go overseas within 48 hours - then there's collections. Some which are pre-12pm collections, others which need to be collected before the business closes for the day - fitting all that into one day isn't easy, especially when your round might include say, 15 pre-12pm drop-offs, all of which are 30 miles apart in different directions!