Because these are the same in all Pokemon usually, The accuracy is determined by the moves, and Pokemon usually have no additional evasion, except during battles the accuracy and evasion can by changed by certain effects.
Becuase every pokemon has the same evasion and accuracy moves have differant accuracy and some moves boost accuracy and evasion and some lower accuracy and evasion and some abilities like snow cloak and sand veil boost evasion in certain conditions
