Because the PayPal donate button is a macropayment that takes a lot of thought and effort compared to Tipjoy.
Also, we're a layer above other payment processors, which means you won't need to use PayPal eventually if you don't want to. Lots of people actually hate PayPal.
It's true that it's easier to donate something with one click. It's also not new to me taht some people don't like them. But money business is a hard business with all the illegal money laundring going on around the world. I wish you the best of luck, but I think it will be very hard competing with paypal
Also, we're a layer above other payment processors, which means you won't need to use PayPal eventually if you don't want to. Lots of people actually hate PayPal.