I’m also confused as to why this is Microsoft-only advice. It keeps sounding like the proclamation involves adjusting an administrative fee for new visas (which, I guess, must be how it bypasses normal rulemaking procedures?).

How does that result in a fee for re-entering on a valid existing visa? Is this less about formal policy and more about Microsoft hedging against the possibility of chaotic and arbitrary enforcement? Which seems not-unlikely when a large bureaucracy has a rule change dropped on it with 24 hours to implement…

See other posts above. The proclamation explicitly states that the fee is due upon re-entry for existing visa holders.