My 85 year old dad has completely given up on using technology. He has always struggled with it, but at least in the Windows 95 / Windows 2000 days, things were pretty consistent: an embossed button, that looked like a physical button, was clickable. A scroll bar meant that there was more. Icons usually had significantly different colors from each other and so were easily distinguishable.
Now days, how am I to explain to him what can be clicked, and where you can drag to scroll? Every app has their own "visual design language", and all try to aim to be as flat, colorless, and minimal as possible. You have to know "secret codes" like where to swipe, to do actions. It's tough for folks who don't live and breathe software every day all day.