In 2019, why is it inappropriate for enlisted and officers to date or marry with consequence?

You're in the reserve component, you're allowed to date an officer as long as it's not from your work. If you don't understand why dating someone at your work would cause major issues, then it can't be explained

If you truly believe in the necessity of the division of commissioned and enlisted personnel, you cannot countenance such unions. Once that divide is bridged in the bedroom, it ceases to exist anywhere else. I know that there are commissioned officers who want to be "familiar" with subordinates. I've seen them and, in every case, they were ineffective leaders not only to their own detriment but also to the detriment of those they led. Command is a lonely space. Responsibility is a heavy load to bear. If you aren't up to the challenges, you should remain among the enlisted ranks.

Can theoretically be married, just can't date, which essentially makes it impossible to reach "married" without having an improper relationship, other than one member of an enlisted marriage becoming an officer after the marraige.
The "why" is because it is codified in Army Command Policy, and the resulting charge could be a violation of Article 92, UCMJ.
It used to be authorized, but was again prohibited 1 March 2000, update to AR 600-20, para 4-14c(2), and remains so with the latest update.