@burcidi-- You're right but companies are aware of the points you talked about. They know that unless they remain competitive by keeping prices low and improving quality, they're going to lose out.
Just because demand and supply are equal in a mature market doesn't mean that new companies will not enter that market. They do all the time! If they can produce the same good at a cheaper price and good quality, they know that consumers prefer them. So they will go into a mature market and drive out other companies that can't compete with them.
If you look at it this way, as long as there is renovation and good prices in a mature market, I think it can last for a very long time. Unless there are some outside factors that change demand and supply.