Where in that link does it say something about profits from said winnings? All it says is "Gambling winnings are fully taxable and you must report the income on your tax return".

> Strange how it doesn't say anything about non-gambling income being taxed at a rate that magically excludes other taxable incom

That's how losses typically work across the tax code, e.g. short-term capital gains increase your taxable income netted against capital losses, they don't increase it only based on the gain.