Is there a limit you see in taxes?
Do you have investments yourself? Maybe you donated all of your investments to the government after realizing how little you were being taxed?
Your last question is silly. The reason why I can simultaneously support higher taxes, yet not voluntarily donate money to the government, is because advocacy of higher taxes can raise far more money for government than my personal donations. Raising money to fund government is a collective action problem; if government relied on donations to run, it would fail because of freeloaders - in essence, a tragedy of the commons. But by collectively enforcing mandatory taxes we can make government work.
It's arguable whether giving government more money results in government working better.
By some accounts government is a demonstration of waist and an exercise in excess.
Government departments are always chronically underfunded, primarily because no government department PR employee ever got promoted by saying "we have enough money".
"The market" not attractive enough - there's nowhere to put your money other than "the market" (including bonds, commodities, real estate etc.) unless you keep it in currency, and that's even more susceptible to government takings.