Pretty much every single short/medium hall UK based pilot has done this sort of duty multiple times in a week at some point. 5 canary return flights in a row from the UK is around a 4:30-5:00 block each time round. Wake up 4am, land at 5pm straight into rush hour traffic on the way home, freshened up and ready for dinner by 6:30. Bed straight after that and attempt to get some decent sleep before the alarm goes again around 8 hours later at 4am. Thats if your neighbours or young kids play ball. Repeat this 4 times over. Done on multiple occasions myself and whilst all within limits absolutely draining.
If it is found that fatigue did play a part then remember these guys were on their first sector! Consider the crew that is up at 4am, 5 hours down to Tenerife and picks up a 2 hours slot and goes into discretion. 5 hours after that approaching home base where the weather is gusting 50 knots, you're both tired and theres a distinct possibility of diversion. This happens and it happens all the time.
Concurs with a chat I had on the ground in Dalaman last year with a pleasant Captain who shared a few minutes of his very limited turn around time with me and my lad (who is hoping to join the RAF as an officer A level results pending) who'd never seen a flight deck up until then. This chap said he couldn't wait to retire, was fed up with automation and most of all was absolutely knackered all the time, that crew were all up at 0400 that particular day. Interestingly he'd made his money elsewhere, had a flying lesson and the rest is history but still desperately wanted out.
Sad and terrifying at the same time.