>>57623838>5 unevolved PokemonAt the end of that battle is when Silver finally recognizes the error of his ways as a trainer, having his team be unevolved is extremely important to show that up to that point he was a loner (no trade evolutions) who selfishly mistreated his Pokemon (no Crobat). Here is his team after that when you battle him again in the post-game, when he's become a better person.
Magneton and Sneasel didn't evolve because clearly Silver doesn't know how items work, Giovanni didn't want to pay for him to go to PokéSchool 