We discussed this prior to launch, and obviously decided to launch as you see it. :) Our reasoning was that a) standardizing on GitHub URLs makes it easier to do automated analysis as part of the funding model, and b) any project important enough to matter will have at least a GitHub mirror. If you have counter-examples to (b), please comment them on GitHub (see what I did there?) or here and I will copy/paste for you. :)
https://github.com/osendowment/endowment.dev/issues/34