The Nebular theory says that spin is a factor. If a star forms with almost no spin at all, very little leftover debris should be present. What qualifies as a ‘planet’? Pluto doesn’t pass only because it hasn’t cleared its orbit. A system with very little leftover debris won’t contain any planets according to our definition.
Can’t afford to stay at a Holiday Inn Express, so I had to look up Nebular Theory. Quite interesting. Thanks.