The problem isn't the back door. Every telecom company in every country provides access for "lawful intercept". Phone taps have been a thing for decades and as far as I know, require a warrant.
The problem is that telecoms are very large, very complex environments, often with poor security controls. Investing in better controls is hard, time-consuming and expensive, and many telecoms are reluctant to do it. That's not great great since telcos are prime targets for nation state hackers as Salt Typhoon shows.
Hacking the lawful intercept systems is very brazen, but even if the hackers didn't don't go as far, and "only" gained control of normal telco stuff like call routing, numbering, billing, etc. it still would have been incredibly dangerous.
The problem is that telecoms are very large, very complex environments, often with poor security controls. Investing in better controls is hard, time-consuming and expensive, and many telecoms are reluctant to do it. That's not great great since telcos are prime targets for nation state hackers as Salt Typhoon shows.
Hacking the lawful intercept systems is very brazen, but even if the hackers didn't don't go as far, and "only" gained control of normal telco stuff like call routing, numbering, billing, etc. it still would have been incredibly dangerous.