Usually you want to use income taxes to discourage particularly high wages, if you take away expenses then this effect becomes less strong, which could lead to

Usually you want to use income taxes to discourage particularly high wages, if you take away expenses then this effect becomes less strong, which could lead to more inequality. Taxing money at the point where it leaves the 'corporate' sphere and enters the 'private' sphere is also a fairly simple way of ensuring there are no loopholes. This is also why tax on capital gains is necessary.