A great reason to try and support small distros is that older computers can still be used as long as they work.

There are also some charities that ship old PCs to Africa, install a small Linux distro on them, e.g.:

https://www.computers4charity.org/computers-for-africa

https://worldcomputerexchange.org/

Excellent point.

When I lived in London I helped clients donate a lot of kit to ComputerAid International:

https://www.computeraid.org/

And what's now Computers4Charity:

https://www.computers4charity.org/