You missed a category of earning.

[zander]

I described it in a blogpost here some time ago;

https://read.cash/@TomZ/how-to-ensure-income-for-crypto-currency-infrastructure-development-b016814f

Relevant excerpt;

Developing money infrastructure is about money
In many ways joining Bitcoin Cash is like joining a startup. They often don't follow 9-5 office hours or get a (big) monthly paycheck. Instead the pay is in stock or options and the harder you work to increase the value, the more valuable your stock will be.
There are a lot of parallels between bitcoincash with startups in that most of the active Bitcoin Cash developers joined without anyone hiring them. It is well known that most of them indeed have savings in Bitcoin Cash and today are working on BCH to make their investment rise in value.
Developers that add utility to Bitcoin Cash literally create value. And the network effect of money means that this comes right back to them in the shape of their holdings rising in value.

That last sentence is likely the simplest and shortest version. Replace "Bitcoin Cash" in there with a more generic term for money and it still works.