The simplistic reloads were one of many things that people remember as being definitively 'Goldeneye'. It goes along with the weapon-bobbing, unrealistically weak weapons, holding assault rifles with one hand, speed strafing etc...
Changing them to realistic reload animations impacts gameplay a great deal and in most cases would unbalance gameplay. Also it would get in the way of the future implementation of duel weapon wielding. As it stands it's functional and nostalgic, changing it would be an arbitrarily bad decision.
