Some people just cannot get on with mobile phones. Can't use them and / or don't want them.
By the way, you don't have to have a landline to get broadband.
You can ditch the BT landline altogether, knock. If you live in a Virgin area you can get broadband without paying line rental.
You could opt for a 'mifi' set up where you get your wifi from a SIM card (£23 a month unlimited data from 3).
i always thought tht having a deal with no landline was more expensive (or at least not cheaper) Plus I have a genuine 60's Bakelite dial phone that I like!
I have a landline with Virgin Cable for the broadband. I do not know my landline number, and neither does anyone else. I do not have a phone plugged in.
When 5G properly arrives, I will probably go the tethering route.