I've always thought, the writers seemed to hate the thought of Ash being "overpowered" and having fully evolved Pokemon at that stage of the anime. He gets rid of Primeape and Butterfree as well, immediately Oak's Muk, and never seems to withdraw Kingler after the league, so his only fully evolved Pokemon was a Charizard (who doesn't listen to him). As I see you seem to be watching the early episodes (for the first time?), I won't add anymore in case you don't want it to be spoiled.
I suppose by the time they finished Orange Islands, the writers didn't see the need for him to get it back because he'd just catch another bird Pokemon in Johto.