I'm swedish and I don't know how common it is here, but the reason I think it's seen as 'very common' is because it's one of the more common kind of allergy
There's pollen, fur and nuts. Pollen allergies are seen everywhere because someone with it often has clear visual symptoms like red eyes and nose.
Fur allergy is not as easy to spot just by looking at the person, but there's a reason why people with dogs are recommended to sit in the front of the bus. Dogs shouldn't be in places where people can't move away from them if they need to.
When it comes to nut allergies you kind of have to ask people if they have it (same with most food allergies), but there's still rules at schools for example that says you're not allowed to bring nuts inside school walls. To me, as someone with peanut allergy, that's great but at our school of 450 there was only me with airborne allergy to it. I think that is one of the reasons it seems to be very common even if it really isn't.
Just my two cents
Take this poison from your mind.
Who knows you might be gone by this time tomorrow and,
I don't know where we're goin