Why wouldn’t more of them simply form like a star with star having the same orbital mechanics, while rogue planets ejectide from a planetary system would tend to be captured elsewhere or escape out of the galactic plane and into intergalactic space?
I imagine that there are copious examples of about everything that might happen to them happening to them. Lots of them would stray too close to a star and be diverted out of the primary galactic orbit.
But once in a galaxy, it might be much more difficult to get pitched out, rather than curved back in. And certain parts of the galaxy with major black holes would be planet traps. Supernovas could knock them off trajectory as well.
My guess would be that I am right, and you are right, and 'it' happens in some ways we can't even imagine.
It is 'possible' in an 'infinite' universe for 'everything' to happen.
Most solar systems are likely a mixture of 'created' and 'captured' planets.
For instance, it has been accepted that most planets in our Solar System are 'created'. However, Uranus may have been captured. It has a vertical rotation, rather than horizontal like the rest.
My main point was that matter surrounding a star would become stratified like the rings around planets, and if that is true, then it would help explain the makeup of the different planets in a solar system.