Earlier quoted context omitted.
There are of course two sides to every coin. The flip side is, cell carriers never signed up to be a secure identification mechanism. SMS wasn't designed for security, and there's little financial incentive for them to invest in those changes, i.e., they don't charge you more for secure authorization of 3rd party platforms. I think its very akin to the US Social Security Number being used as a 'secure' identification…
That's a good point in general; NIST recommends not using SMS for challenge-response authentication. I don't know whether in this case the victim was using SMS codes, or whether the attacker used their phone number as part of a more involved attack (e.g. calling customer support and impersonating the victim). Even if you don't use SMS codes, there are a number of attacks that are opened up if someone seizes your cell…
Usually the attack is done against an individual who is known to have significant crypto assets and is using Gmail. By default if you enable 2fa on your Gmail account, sms based 2fa is activated as backup.
The attacker social engineers the phone provider to port the victims number, then resets the victims Gmail account, uses Android device manager to wipe their devices, and using the details found in Gmail they proceed to gain access to other accounts owned by the victim. The main goal being to social engineer access to services where they store crypto or to find unencrypted wallet backups in the cloud.