It's hard to empathize with abstract people, you need to observe and engage actual people in their environment, which costs time and money. Too often people are stuck in a conference room talking about personas. I've ended up frustrated at clients telling them "you are not your customers" endless times.

It's amazing how much you learn getting out and talking to customers. One of my favorite examples is for a company that sold plumbing supplies to contractors. The biggest feedback was that these guys spent most of the day in a truck and needed to be able to place orders on their phones and they begged the team to make sure that all the buttons (and links) were much bigger so that their fat fingers could click on them: "this was designed by a pianist".

There's so many examples of interactions that show that the designer didn't understand what the end user is really trying to do. My bank makes me enter a first and last name for transfer recipients, but only use the last name on the confirmation step, however the bulk of my transfers are to family members!

Personas are a massive improvement over designing for yourself or worse designing for what's fun to design.

Are they?

If you design for yourself at least you are using a real person. Personas are invariably about the same as designing for what's fun.

Absolutely, it's that plus the fact that young designers and programmers crank out much more output. And they're cheap.

Myopia and hand aches give excellent perspective on the problems of accessibility in UI design. Alas, they also tend to limit my time with the machine and productivity in that time.

It's about the same how Reddit users' average age is purportedly twenty-something but the content and comments are dominated by teenagers. Teens just post way more.

Ultimately, accessibility for the elderly is a typical case where one has to invest additional effort by choice and principle. I.e. not gonna happen under just the market forces.

More output means more bugs.