Yes, banks calculate that with 5% the costs are not higher than 33% of your income.
Currently, interest rates are very low and make up much less than 33% of people’s income, what makes real estate quite affordable at the moment. However, we also know that these affordability calculations are very tight and 33% or 1/3 of ones income just for housing is actually a very large part of the pie, and that many people buy real estate even though they barely can afford it. People use all their savings, sometimes even their pension funds (2nd pillar & 3a) just for the sake of owning property and literally ruin themselves like that.
We also know that many people live beyond their means, e.g. they have expensive cars, suddenly they have 1-2 or even 3 children which are expensive, maybe pay for a private school for children or their piano or guitar lessons, go on holidays regularly, have expensive hobbies, eat in restaurants quite often, or whatever, so many people don’t have much money left at the end of the month and their savings are very limited. So if now their costs for financing their property significantly increases, it will constitute a big financial problem for many and they can’t afford it anymore even though the bank calculated with 5% but didn’t take into account that the living situation may change.