Given that they were converging, with the Metroliner just below the Cirrus (as it hit the top), it could be one of those unfortunate occurrences where a) there was a constant relative bearing, and b) the nose of the SR22 might have partially or wholly obscured the view of the Metroliner.
The SR22 pilot would have likely been concentrating more on the runway than anything else, same goes for the other pilot. Short finals is a classic area for conflict: it’s not at all uncommon for aircraft to get really close without realising, especially when one is just above/below the other.