A plausible source of these sorts of things is that some government(s) fund their intelligence service to do signals intelligence, but intelligence services com

A plausible source of these sorts of things is that some government(s) fund their intelligence service to do signals intelligence, but intelligence services commonly have no morals or accountability because they operate in secret and claim national security whenever anyone comes to question their activities. So they use the money to lobby for mechanisms to have backdoors or chokepoints installed, or require vulnerabilities the equivalent of backdoors, and use dirty and illegal tricks under the table to get them passed. The governments they're lobbying usually aren't even the ones paying them, though maybe sometimes they are. It's basically the equivalent of Dual EC DRBG but targeting the legislative process instead of a standards body, and obviously an inherently difficult thing to prove in an individual case, but the response to it should be the same in any case: Don't pass laws that would be to the advantage of a foreign intelligence service. You certainly don't want to give them the damn thing whether they're the ones pushing for it or not.