They don't do that, they just lie.

https://tip4commit.com/github/django/django

    Project maintainers have decided not to notify new 
    contributors about tips and they probably don't like
    this way of funding.

Then they return the tip to the 'project' pool which is themselves for unclaimed or unwanted funds:

    Funds that are not claimed during 30 days get returned 
    back to the donation pool of the project

The donor is deliberately deceived about whether the person or project will ever get the money.