They like it because it’s cheap and easy. They pay a phone provider for the 4 digit phone number and type in a script to generate a random code and text it. There is no oversight or maintenance.
Pairing with an Authenticator app is easy, but a little more work. Pairing with a mobile app can get a little tougher and require development plus maintenance in making sure the app cannot be spoofed and works with updates. Using a physical drive for 2FA is a pain in the ass to set up. From a business standpoint, 2FA only needs to work enough to remove liability from your business. If someone spoofs your cellphone number that’s on the phone provider not them so that’s enough to remove liability