In some countries not necessarily. I’m based in Czech Republic and as a sole proprietor the most preferential way to do taxes (up to certain threshold) is to report the gross income and use a tax rule that assumes that it cost you 60% of gross revenue to get your income. In this case the lower income shown the better.

So you've spent 10% and are 50% up. Isn't that already advantageous enough for you?

Taxes fund a civilised and (mostly) well run society that you benefit from. Misreporting your gross income shifts more of that burden onto your friends and neighbours!