Because barriers to entry protect incumbent firms and restrict competition in a market, they can contribute to distortionary prices.

Customer loyalty - Large incumbent firms may have existing customers loyal to established products.

Keep the borders of the economy open to support free trade and maintain a high level of competitive pressure on incumbent firms.

Access to the same level of technology (to incumbent firms and new entrants)

When the original incumbent firm(s) respond by returning prices to levels consistent with normal profits, the new firms will exit.

A way to achieve this is for the incumbent firm to constrain itself to produce a certain quantity whether entry occurs or not.

Moreover according to Stigler regulation can be captured by incumbent firms to protect the market from the entry of competitors.

For example, there are documented cases of pre-emptive patenting by incumbent firms.

In addition, incumbent firms have actively carried out strategic moves.

Product proliferation is often used by incumbent firms as method of entry deterrence.