The unfortunate result of allowing anti-intellectuals to participate in governance....
A result of Politicians who want to control something they just don't understand. Even worse they don't possibly comprehend the choices of their decisions. It's a bit of a hypocrisy that Congress doesn't care what happens with spying, just as long as it doesn't happen to them.
That said, secrets can be exposed and hard to remove. (ie: Eternal Blue/Wanna Cry) and the ramifications ever lasting. The weakest link isn't the technology, but the people who use it and maintain it. People make mistakes. It's part of human nature. And the devices made by man (including back doors) therefore can be inherent with bad design choices including exploitable ones. No amount of code reviews, design, and security procedures can stop the weakest link: A dumb person (IE: A contractor who installed cracked keys on his classified laptop.) Or a politician who doesn't even listen to security rules (IE: Hillary Clinton's private email server)
There are only two remote controlled systems that are critical and can't be compromised. (Power plant controls, and our nuclear defenses) Why? Because there is no complete digital point A -> B and the technology is proprietary to just one specific system. The final end point of said commands is controlled by a human being. They are the ones who manually throw the switches on an isolated system. Quite simply compromising a device through a digital chain opens it up to remote compromise by threat actors.
It's entirely possible the back door can be exploited by other actors who the government did not intend. For example, a Russian, North Korean, Iranian, or Chinese hacker group may compromise someone in a sensitive position here in the USA. Look how WannaCry and Stuxnet type viruses were used against the public after they were exposed. There are always new ways to exploit once was thought safe. That includes encryption (WEP/WPA/TLS 1, etc...) and APIs (SMBv1, Struts) , languages (Javascript) and hardware (RowHammer/Spectre/Meltdown)
And to be honest they don't need more back doors. They solved a lot of these problems YEARS ago. They don't try to get around the encryption. They just compromise the end point where the end encryption happens. This way you have full access to that data and everything on that device that might be related.
Theres also another unintended side effect: If backdoors are suspected in your product, then the customers in question will move away from your product. There's a reason China is creating their own OS and CPU chips. And there's a reason the USA refuses to use Huawei isn't allowed to sell 5G infrastructure to the USA.