why to we need to continuously improve business processes?

Answer 1

Because quality & quantity are very important in order to stay in business and don't get eaten by the giants or even baby giants in your locality.

Your competitors are doing it! So if you don't, well you won't have any customers left after a while, because they will find better value for their money elsewhere!

Answer 2

Your competitors are.

Your customers are being approached by your competitors - customers therefore expect improvements.

To increase profitability for ownership.