Almost everyone does the math right, it's really pretty simple, takes a few seconds to calculate, and once you know parameters it just doesn't get easier, it's 5th-grade math at best, but what EVERYONE doesn't have is a crystal ball, if difficulty doubles half way it means only the first half of your bitcoin matches the current figures, the other half will be 2x more difficult which makes the overall calculation off by 50%.

Also, none of the parameters used in the equation is constant, not even the power rate we pay today is guaranteed to be the same next month, so you have an ever-changing difficulty figure, a variable power cost, other unknown costs, all of these models are hardly accurate, you can save today's numbers and look at them a year later, you will laugh at how inaccurate they were.

An example, many people who bought the 17 series when they first landed thought they would recover their investment in 6 months, it has been almost 3 years now, most of them are yet to see ROI (including myself), if you told anyone the same shit back then, they would think you are crazy, if you tell someone today that paying 0.25 BTC for S19 is going to look terrible next year, they will laugh at you.

So long story short, nobody knows how much it will really cost anybody (not even themselves) to mine bitcoin.