The ulterior motive behind the Borg not wanting its members to not date/marry non jws is,,, the Borg needs the craziness us vs. them mentality to continue. And the like-mindednes to resume.
Its always loyalty,loyalty & unity ,unity & unity & the donations$$$$ keep rolling in.
They cant have any diversions.
Any jw breaking the mold is dealt with the threat of being kicked out or labelled as "bad".