Let’s clear this up real quick: it ain’t swapping the SIM card of your phone; it’s swapping the SIM card of your phone number.
That’s a SIM Swap Attack: when your phone number all of a sudden belongs to somebody else’s SIM card instead of your own.
This is usually performed by calling your telecom and pretending to be you, telling customer support that you’ve lost or destroyed your phone or SIM card, and that you’d like to keep your phone number by porting it to a new SIM card. This is a standard and routine service provided by some telecoms (not mine) to customers. But as you can see, it can be abused by criminals to steal your phone number and use it for other attacks, like bypassing 2FA.