Isn’t it less of a government backdoor and more of a result of generally old and insecure protocols still being in use for telecom?

Like, the phones happily connect to these fake towers because the signal is strongest from that one and there is no authentication to verify who the tower belongs to, nor encryption of SMSes?

It’s not exactly a back door. It’s a fake radio cell, mimicking your network provider and acting like a man in the middle. In that sense, it’s like a stingray. The differences are

1. The Stingray eavesdrops, but avoids interfering with user traffic

2. The stingray is operated by law enforcement, not by fraudsters looking to steal your money