Airports have got worse since they stopped having separate check in desks for each flights, rather than a free for all. Not sure if that still happens with some airlines but in my recent experience, particularly at Manchester you have all Tui customers for example in the same queue, regardless of flight time.
There has got to be a more organised way of doing things, surely. As always though, a lot of the time its down to people making things busier. Now people are worried about queues they will get there earlier, thus making it worse. Not exactly thought this through but maybe each check in desk has security directly behind it, then you go through straight after dropping bags, might take longer initially but at least you are only queuing once. Then obviously a separate one for anyone not checking in bags.