Most parasites evolved from more complex species. They gradually lose the ability to produce for themselves what they are taking from their hosts.
Case in point: Dodder
Dodder has lost the ability to photosynthesize it's own food. It sucks its food out of others.
The similarity to Trump and his uber-wealthy supporters is pretty clear, don't you think?
As workers become more productive, the uber-wealthy take all the profits and then some, hording the money in ways that do not improve the lives of those who actually created the wealth.