As we all know that Samsung launches the A series around March every year. So the A73 is due in March and it will come with Android 12 out of the box. To get people to upgrade to A73, Samsung will probably postpone the A72 Android 12 update after the launch of A73. In my view, Samsung will update the A72 to Android 12 in April (one month after the launch of a73).
So everyone, be patient! :)