Don't let the perfect be the enemy of the good. We can and must improve things iteratively. Just because we can't fix everything doesn't mean we shouldn't fix anything.
The difference between governments is who is getting the tax breaks. Progressive governments give tax breaks and stipends to ordinary workers, while conservative governments give it to corporations and the wealthy.
In order to gain or stay in power you need to make sure your key supporters are looked after. This is as true in dictatorships as it is in democracies.
Isn't that an oversimplification, though? Governments also use tax cuts to shape behavior.
If you put taxes on speculative trading, such traders won't vote for you -- but people who are against speculative trading will. If you give speculative traders a tax cut, the inverse happens.
It also obviously will shape behaviour, but if that was the only purpose then the government wouldn't be fulfilling their primary purpose: trying to stay in power as long as possible so they can achieve whatever they set out to do.