Companies are trying to gain market shares to increase their profit margins. The reason for this is fromthe dividends. If a company wants to see more income than they can buy another company's stock shares and they can also sale their own stock shares. If a company does both they will be getting more

If a company does both they will be getting more market control leading to monopoly in the market.

Explanation:

In a every business endeavour, the aim of every company is to maximise profits while losses are minimised greatly to the bearest minimium. The only way to achieve this is to apply series of principles leading to dormination of the market (Monopolisation of market).

This could be achieved through buying of other companies stocks when the prices are at the bearest minimium while at the same time selling their own stocks when the prices are at the highest point in the trading platform.