Some speculation for you: (Based on what I've seen online and random other #facts)
El Salvador was already dollarized with no central bank of it's own. It started a step further down the road than Argentina is, and had no central bank to fight bitcoin.
If Milei tried to run his campaign on a promise of replacing the central bank with Bitcoin he would have gotten much more pushback, maybe a few bullets to the head, and still it would have been unrealistic to think so much could transform in 1 presidency.
This way, removing the central bank first by dollarizing, then going to bitcoin next, is the best way forward for Argentina. Maybe he can produce some state-sanctioned bitcoin mines & stack a few sats for the treasury long before any major BTC adoption push.