because the Falcon Heavy isn't out of development yet. And because it relies on the Falcon for parts. So getting the Falcon running perfectly is first priority

because the Falcon Heavy isn't out of development yet. And because it relies on the Falcon for parts. So getting the Falcon running perfectly is first priority. And because not every payload will make sense for a Falcon Heavy, there will probably still be a logistical need for a smaller rocket. And last but not least, the Falcon price will probably come down once they get the re-landing legs working.