It is said in the East that saints have to consciously tone down the grace that shines from them, lest it overwhelms people.
I would imagine that after Jesus rose, the grace that blazed from Him was so enormously powerful that only those closest to Him, and most purified, could stand it. Perhaps it’s not that He didn’t appear to others, but that their consciousnesses literally could not stand to witness His power, and shut down. They probably got sleepy... or later simply didn’t remember anything... but in any event, it was simply too much for them to bear.
Plus in the east, where the sun rises, it is the sun, at its brightest first thing in the early morning.