One reason I see hardly mentioned is change of tech stacks. Most modern developers do web development with a highly abstracted stack (including yours truly).

One reason I see hardly mentioned is change of tech stacks. Most modern developers do web development with a highly abstracted stack (including yours truly). So nobody is much familiar with C / Perl / OS level APIs. Closest they get is adhoc shell scripting in form of devops tools. Since people are so much abstracted from the stack, they don't feel much need to contribute to it or improve it to scratch their own itch. That's why new stuff like CNCF gets many contributions, old ones like Debian don't.