What is backdoor and why is it created in first place if it creates additional unnecessary risk? You might want to take up an example to explain it in detail.
A backdoor is a way to get into something, like an application. Many are written as administrative tools so admins can access a system even if users have broken the main entrance.
Some backdoors are secret, so the person running server or application doesn't even know someone has access to it. This can be malicious - obviously for an attacker, having a route in is useful but if the victim knows about it then they can try to fix it.