Actually decreased demand isn't the only scenario. If you knew anything about business you would know that. A couple of other reasons include exchange rate (if you are international), having to lower prices due to increased competition.
All you need to do is look at the Reagan years. When he cut taxes, revenue to the treasury increased. That is a fact. When Bill Clinton cut taxes on the rich by dropping the capital gains rate (something liberals always seem to forget) revenue increased
That gobblement SPENT those increases is a separate issue.
It is like you getting a 5% increase in pay every year but increasing your spending by 10%.