The things nobody wants to pay for

Indeed money donated to Debian is not used to pay for the time of Debian developers/contributors. It might be used for hardware, hosting, travel reimbursement, debconf organization, and that kind of activities.

<shameless plug>
With Freexian we try to help fill that gap. Thanks to the various LTS offers, we are paying Debian developers to work on Debian. This is part of our mission and we are regularly reporting our activities:
https://www.freexian.com/about/
https://www.freexian.com/about/debian-contributions/
</shameless plug>

For now, it's the margin on the various services that make this possible but we are considering to add some broader offer that would also encompass the "please take my money to contribute to Debian and make it a bit more sustainable" use-case.

I'd be happy to discuss with companies that are looking to contribute to Debian in such a way to help refine our future offer.