This is an important question. Products should be consistently reviewed in many different ways - in comparison to the markets as well as profits. There are several reasons for this. I will mention two.
First, products evolve. This means that certain products might sell well at a given time, but this could change. In other words, new products are introduced and these replace older ones. When this takes place, older products do not sell well. Hence, it is imperative for companies and vendors to constantly check if products are selling well and what other products are being offered. All of this will have a bearing on profits.
Second, other companies play to win. So, they might sell their products are a discounted price. When this happens, they might control the market in the future. So, a wise company or vendor will always be aware of their competitors.