You don’t just shove a guy into a position he’s never played before. First base may be the easiest position to play, but there are still techniques and plays that need to be learned. Throwing anyone in there with zero notice is detrimental to the team, and that is is something a manager needs to avoid.
I remember when a need arose at 3B many years ago. Yaz (a great LF and a decent 1B) volunteered to man the position. It was an utter disaster.
Should Rafi start taking some infields and working with the coaches on footwork, etc? Probably. In a game less than 24 hours after the injury? No.