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.
Your comment assumes smart people stop learning things when they get old, which is demonstrably incorrect. I also doubt your statement that many changes have happened because old people died. I suspect new minds had more to do with making changes than the old ones dying. And it is unknown if we would have had more or better changes if people had longer lifespans.
Being "old" isn't necessarily a question of age.
There are 30-year-old "old" people who don't want to learn anything they don't already know. And there are 80-year-old "young" people who gladly learn an interesting new tech.
140 year old Albert Einstein might have written an actual letter to 161 year old Max Planck because that's what they both knew and had known for more than a century, so why change things? Many of the technological and societal changes have come up because of old people dying, including the smart ones.