For giving out XP at the end of every session would be a pain. The end of sessions are already always a pain. We are always hurrying because we are about to (or already have) gone over time. Often we are mid-adventure, or even mid-combat(!) which means we have to carefully note everyone's hit points, remains spells/slots, position on the map, etc. . . So trying to add giving XP to that or (worse to my mind) stopping the flow of the game to award it as it happens would not be to my taste.
The best I can imagine with those approaches, if I were to try one, would be awarding XP for the last session at the beginning of each session or awarding it via email between sessions.
I guess I am also old school in that I always imagine going up a level required some downtime in addition to XP.