Why Isn't Paypal More Successful?

I just bought a replacement part at an online store I've never shopped in before. I was dreading the checkout process since I have not committed my various credit cards to memory. But thankfully this store offered checkout with Paypal. I clicked on it, entered my paypal credentials, and was out of the store in less than a minute.

It was an awesome experience, as simple and easy as checking out at Amazon. 

And yet, Paypal has not really taken off among my friends and family as a way to pay for stuff online. The Gotham Gal doesn't like Paypal and avoids it at all costs. I find that most people I know feel the same way.

Why is that? Is it that Paypal works like a debit card and the money is taken out of your checking account immediately? Is it that the Paypal implementation used to be clunkier and most people have bad memories of failed checkouts? Is it that most people have committed their credit card info to memory and don't mind filling out the web forms? Or is it something else?

All I know is that when I see a checkout with Paypal option, I take it every time. And if everyone else did, Paypal would be so much bigger. But it's not. And that's worth thinking about. Because there is a very big opportunity to reinvent the way payments work and Paypal is front and center in that opportunity.