Why do they need a huge profit margin of profit is the money left over after they’ve paid their expenses?

Because if they were taxed on revenue, not profit, they would have a higher tax burden than their profit and go bankrupt

And why wouldn’t you want the same system for individuals?

If you could deduct all your expenses from taxes the only ones paying taxes would be people saving up their money. I also didn't say with a single word that I don't want the same system for individuals, why are you arguing in bad faith and putting words in my mouth?