You should look at the Snowden leaks sometime. They had cooperation, including backdoors, in a large number of companies' products and networks. RSA cost them about $30 mil to risk whole market. For carriers, usually around $100 mil or so.

Also, remember that it's easier to do if you disguise it as a coding flaw. It wasn't a backdoor: just one among many flaws accidentally hitting our systems. Wouldn't cost any market share.