But taxing on gross means that you penalize low-margin companies.
Take two basically identical companies. They sell, say, computers.
One company has a "luxury" brand and they sell 1 million units at $2,000 a piece with a $500 profit on each. They have gross sales of $2 billion and profit of $500 million.
The other company has an "economy" brand and they sell 5 million units at $1,000 a piece with a $50 profit on each. They have gross sales of $5 billion, and a profit of $250 million.
The luxury company is taxed at 1%, and the economy company is taxed at 5%. The economy company's entire profit is eaten by the tax, so they must raise their prices to $1,050. The luxury company may or may not raise their prices at all -- if they do, they raise them to $2,020, maintaining their profit level.
We have effectively propped up the luxury company's business model. They have reduced the price differential between themselves and their competitor, and the people paying the difference are the tax-payer. Why did we do this? Do we like corporations having very high profits? I'm not aware of that as being a national goal.