The vast majority of systems are mounted with short standoffs (6in) to the roof surface. Changing to a tracker would probably cost double or more. You save massively on installation costs when you can take advantage of west/south/east facing inclined planes that roofs represent. Also consider that many customers have upwards of two dozen modules, so it's no small feet to move all of them.
The reason that systems face south is to maximize overall production. The best solution is to combine this with a storage system so that all that great production can be buffered and meted out as needed over the course of a whole day.