It is a conflict of interest that allows them to gain a disproportionate amount of control over the market. It causes direct harm to competitors, through both t

It is a conflict of interest that allows them to gain a disproportionate amount of control over the market. It causes direct harm to competitors, through both the access to confidential sales data and access to the market. It also causes harm to consumers (at least in cases of locked down platforms like iOS) since they no longer have access to competitor's products. In short, it is no longer a free market.