I was wondering the same thing : why do you need a 3rd party site/service to do this? If you're a software developer then setting up something to get donations via PayPal or Stripe is easy.
The network effect can make a reasonable case. Similar to how many open source projects benefit from centralized hosting options (e.g. github), projects can in theory benefit from more centralized funding platforms.
PayPal and Stripe are 3rd party services as well ;)