>>15346671Ash has no control over his Pokémon evolving because levels don't exist in the anime and Ash rarely catches Pokémon that need an item/trade to evolve. Ash's Pokémon evolve based on their own experiences, often it's their determination to win that results in evolution.
As for the few he could control the evolution of...
- Pikachu doesn't want to evolve
- Gligar DID evolve and said evolution was only delayed so it could conquer its fear of heights
- To the best of my knowledge Ash was never informed that Boldore evolves by trading
Also Ash has plenty of fully evolved Pokémon.
