>>41636928 (OP)
I've realised that in myself that though it is a genuine preference, it's rooted in insecurity.
Being with someone who's a totally dependent mess really asks very little of you. They may ask alot of you in terms of attention and reassurance but they don't challenge you to develop much beyond the role of a caretaker. Being with someone who's striving towards their dreams might challenge your ego and sense of security in the relationship, knowing they could probably trade you out if they desired to.
If you've got abandonment issues, or if your self esteem is dependent on superficial or external factors like work/income/looks etc. Then you don't really have a foundation of innate self worth to build any of that stuff on top of and it becomes only a very fragile situation. Perhaps you only want a simple, slow, gentle life because a higher pace scares you and you just crave that comfort. Then you'll be looking for someone who's after the same thing.
It's all issues with trust/control and issues with self esteem and motivation.
If you've got a girl who's striving. Never get in her way. Support her, encourage her and be ready to let her fly.