Why don't all champions have critical strike animations?

Before I continue, I fully realize that this is NOT a priority of Riot's, and I'm not complaining. However, I'm a little curious as to why some champions don't have a different animation for when they critically strike. A couple of examples:

(Which is really funny because old Karma did have one...)

Now don't get me wrong, none of these champions even build critical strike items; I get that. It would just be really cool if they were given custom critical strike animations sometime in the future, as those animations usually look really cool ( ).

Is there any possibility of implementing critical strike animations for the champions who currently don't have them?