If you rent out a property for 30 years at same rate as your total expenses including mortgage payments then sell it after that point your profit is not actually zero for 30 years then the full value of the house on the final day. There are actually a lot of different ways you can record such a transaction each of which have different trade-offs.

This is also why asset depreciation is considered an expense. https://en.wikipedia.org/wiki/Depreciation However, it may also be recorded as income with the initial purchase being considered an expense.

PS: There are an insane number of useful ways to run your personal books, and a few legally required methods in various situations. But, IMO your goal should be match the underlying economic situation of your enterprise not simply move numbers around based on an abstract formula.