I assume you're young? Finger capacitance can reduce quite significantly with age.

You can tell that most touchscreen interfaces are designed by young people.

Not just young people; young people who have lived in a high tech bubble their entire lives. Most designers are completely out of touch with their users these days.

The users that are young people who have lived in a high tech bubble their entire lives?

I worked on a (desktop) telephone for the hard of hearing. It had a touch screen. Our customer base tended toward older people. We had problems with them being able to register a touch on the screen. We called it "cadaver fingers" (not in front of the customer). Yeah, it's a real problem.