Part of the reason that flying can be stressful, is that for many people, airports are not somewhere they regularly visit.
Consider a person who has been living in a small village in the Highlands of Scotland, far from anywhere like a town. Now take that person to a huge branch of Tesco at peak time on Saturday afternoon and tell them to shop for a family of four in an hour - the results are unlikely to be pretty.
Those who make their way through the same airports on a regular basis learn their way around the system - they figure out which security queue is likely to be shortest, where to get the best cup of coffee, how to get to each set of gates, etc... effectively they have learnt the system and are capable of making it partly work for them, much like those who always shop at the same supermarket and have built a mental image of what items are in which aisles allowing them to get in and out of Tesco quickly with minimum fuss.
Those who fly once a year tend to forget the airport layout after 12 months, and find the whole experience very different to their normal weekly experience. You can put up as many signs as you like, but learning a new system is hard work for anyone, especially when their expectations do not match reality.
Flying Ryanair from Stansted at 7 am on Saturday morning is not particularly user friendly, but if you've done it dozens of times before, you know what to expect and tend to learn how to navigate it with less fuss.