The reason why.
All of the cards in each deck add up to zero in a balanced count, hence the name. When the count is positive, the running count must be temporarily converted to the true count to determine just how valuable that positive count is.
Unbalanced counts are designed to make counting easier by eliminating the true count conversion. In KO, each deck adds up to plus 4.
KO starts off indicating an exaggerated negative situation when too many cards remain undealt to gain much of an advantage anyway. KO then slowly climbs up as cards are dealt since every deck adds up to +4. If the remaining cards are rich in big cards, KO would have climbed faster than average. When and if the KO count goes sufficiently positive to indicate a desirable situation, penetration has also been achieved to fairly match the positive indication.
This is why you experienced your positive counts primarily late in the shoe. If every card in the shoe were played, it would always end in a positive count.
KO is a proven, effective count. I recommend it to any casual player who wishes to have the edge over the casino, but wants to enjoy his play, and has no interest in further advancing his game.
If you think that you might take up other advantage play, you made the right choice by switching to a balanced count, especially Hi-Lo.