Could part of the issue also be that there may not be a large body of foreign players available whom qualify to play in the league or relocate? US, latin & South america, Africa (excluding s. africa), Russia and a large part of Europe & Asia do not have a strong cricket program because of lack of influence from the UK. Those nations that have a strong cricket program (India, UK, Canada?, Australia, S. Africa) may already have plenty of league teams for their players of qualifing caliber resulting in few players of professional caliber not on a team? Just a thought from someone outside of cricket, could be wrong.
I would think maybe they would be the same reasons there are few foreign players on NFL teams.