Oh okay then, thanks for the explanation. I thought the refusal was even before he met LT. Surge. Although we all know the real reason is marketingHis refusal to evolve happened after he went from Pichu to Pikachu. When battled Lt. Surge's Raichu and lost badly, everyone started doubting him until Nurse Joy approached and offered them a Thunder Stone. He slapped the stone away when Ash was about to use it and started, which Meowth translated as Pikachu wanting to prove he can be strong without needing to evolve, which he did as he beat Raichu in their second battle. And since then he's always hated the thought of evolving, a trait the anime staff'll likely never get rid of.
This is never gonna happen, but it'll be funny if Raichu suddenly becomes even more popular than Pikachu. I could see Pikachu doing a complete 180 on his mindset just so they can start having Raichu around lol