Most likely it's because you either indicated the property was less than 100% business use, and/or you indicated personal use days greater than zero, when there were no personal use days.
Regardless of what date you converted the property to a rental, as of that date it was ONE HUNDRED PERCENT business use, if you did not live in the property for any personal use reasons for one single day *after* you converted it to a rental.
Additionally, if you did not live in the property for one single day *after* you converted it to a rental, then it was rented "the whole year", and you have ZERO days of personal use.