LIDL advertise these kilts not for formal occasions but for informal times such as a football or rugby match or some other less formal event. In the past I have had an expensive kilt damaged at a rugby match, costing quite a bit to repair.
These cheap kilts allow people like me to wear the kilt more frequently without fear of damaging possibly your most expensive piece of clothing in your wardrobe.
Also it allows for less well of people to own a kilt for the first time in their life and being able to wear it when they want.