[PeterisP]

The rate of taxation depends on what is the maximum possible rate, what is the available surplus that can be extracted while still enabling the workers to survive and 'reinvest' in things that affect productivity.

In earlier times a farming community of e.g. 20 farmer families simply did not produce enough surplus to feed 20 other families; if someone would tax them half of their harvest, then they would starve, eat their seed grain and breeding animals, and there would be nothing to tax next year. A 10% tax was probably the limit of what could be sustained long-term.

On the other hand, as people become more productive, it became possible to devote a larger share of that production to goals beyond the survival needs of the household.