The issue is partially that while social engineering countermeasures that could help prevent sim swaps could be helped by better training and more rigorous security checks, there are actually bad actors who are employees of the carriers who can be paid off to switch SIMs.

I just had my AT&T sim swapped two weeks ago. According to police, the sim swappers are insiders at the telcos or have compromised corporate credentials and are logging into the telco admin portal and processing the swaps themselves.

I’ve now switched to Google Fi. I’m banking on the assumption that Google doesn’t keep an admin portal open to the internet and that they don’t give sim swap/port access to employees that aren’t paid well enough to be willing to take a small bribe to swap the sims.

I'm pretty sure 611 works without a SIM card.