Maybe because email is far better than physical mail on any axis not primarily driven by nostalgia? Take a look at the actual old people around you, they all use tech too.
All the old people that I know at even half that age do not use any tech they are not familiar with (so yes to a landline telephone, no to email). Perhaps you live in an area with very progressive old people.
My grandfather is 91 and uses WhatsApp and YouTube daily. He grew up in rural Romania, and his formal education stopped after middle school.