It's probably because of the Qualified Business Income (QBI) deduction. You probably have carry-forward passive losses on your rentals. If you don't list rental expenses, the profit on your rentals increases, but you don't owe tax on these profits because of the carry-forward. Then you would get a QBI deduction of 20% of those profits. As you add expenses, the profit decreases, and the QBI deduction goes down, thus raising your taxes.
