As a former serviceman, I will give you my guess as to why it was allowed so long: (caveat: this is not my personal endorsement of any policy, only stating why I think they did it)
Basically, it was allowed under a "boys will be boys" kind of attitude. That, and if they made it an offense chargable under the UCMJ, and they were all going to do it anyway, they were just setting up servicemen to be blackmailable, which could compromise those with a security clearance.
Things like the Tailhook Scandal helped correct that vision, and with the widespread human trafficking rampant in the world today, it is better in the view of the US gov't to take the moral high ground in this case now.
As a former serviceman, I will give you my guess as to why it was allowed so long: (caveat: this is not my personal endorsement of any policy, only stating why I think they did it)
Basically, it was allowed under a "boys will be boys" kind of attitude. That, and if they made it an offense chargable under the UCMJ, and they were all going to do it anyway, they were just setting up servicemen to be blackmailable, which could compromise those with a security clearance.
Things like the Tailhook Scandal helped correct that vision, and with the widespread human trafficking rampant in the world today, it is better in the view of the US gov't to take the moral high ground in this case now.
It's very simply, many wives have complained about guys bringing back STD's.
Recruit the soldier, retain the family.
Believe me, I work policy issues like this full time.