Because the patches are meant to fix the errors players encounter while playing Sims. 你 can choose not to if 你 like, but then your game will be laggy, while it could have been fixed if 你 just clicked that small update button.
Besides, 你 won't be able to install expansion packs unless 你 update your game. An outdated base game when combined with an updated expansion pack will cause corruptions while playing. Trust me, I know. Bottom line, they need to be of equal versions.
