8. End of the Collective
Okay, earlier I mentioned the Borg Queen and while I said dont get me started I have to mention her here and *spoiler alert* a bit later as well. Her very existence wipes out one of the major elements of the Borg---the collective. From their introduction, the Borg were a collective consciousness, a hive mind. They had no single voice. This is, in fact, the reason that Picard was assimilated in the first place. In First Contact that is heavily referenced and then retconned into irrelevance because apparently the Borg have had one single voice all along! The collective has been nothing but the tool of a singular villain. A puppet master, if you will, that has been pulling the strings of the drones all along. From this point on the Borg ceased to become the enemy we were introduced to in Season two of
Next Generation and they became another run of the mill villain with weaknesses to exploit. This may be, more than any other reason on this list, the thing that ruined the Borg. Still, on to number 9 we go!