@Faruk, there are many reasons why businesses would give discounts to their customers at a certain point of the year and not apply a year-round discount.
(Note that I’m not referring to the giants such as Amazon/Wall Mart etc. but to smaller businesses)
First, this can create engagement with customers. You can run a time-limited promotion just in order to great a small buzz around your product and get multiple people to mention this to additional people.
Second, this can be useful for accounting purposes, but that really depends how you run your business and audit your books.
Third, we see it as an act of “Thank You” or appreciation to our customer and the community.
Some businesses can probably permanently use a 50% discount, I’m sure about that, but in general it is not sustainable in the long term for smaller businesses.
Just my 2 cents.