That's just bad writing.
Seconded
The whole "Cortical Implant" was a piss poor way out for the writing team to explain why Seven Of Nine isn't more "Emotional", changing their minds once again they decided that it could be removed and thus an entire episode "Imperfection" was made pointless, I guess another example of the "Reset Switch"
Generally speaking, although i'm a fan of VOY, the parts that did ruin it for me, were generally to do with how the writers handled Seven Of Nine's character
Braga said in a dvd interview that "Imperfection" was supposed to be the beginning of a tragic arc for Seven culminating with her death (to save the crew) in the finale. While I'm not a fan of Trek character deaths considering what they ended up doing to her character in the second half of the final season this arc may have done her more justice.