Counting principal as a rental expense to estimate cash flow

[Account Closed]

Hi, I'm really interested in learning to analyze deals/properties for future investments. I've noticed in pretty much every analysis in videos and blogs, the person will deduct the entire mortgage payment (interest + principal) as a rental expense, before going on to calculate Yearly Cash Flow.

But the principal is NOT a tax-deductible expense. So why is it included as an expense in their calculations? Perfect example, see here: https://www.biggerpockets.com/...

Shouldn't the calculation actually be:

Yearly Cash Flow = ( (Rental_Income - Tax-Deductible_Rental_Expenses - Depreciation) - Taxes ) - Principal_Payments)

If I'm wrong, tell me why. I just don't get how the principal (a non-tax-deductible expense) is always included as one of the tax-deductible rental expenses in all these calculations. It makes no sense to me. What am I missing?