With the declining PVP population, the problems caused by allowing duo-queuing in ranked is more evident than ever.
For the uninitiated, here are the issues it causes:
1. Duos inherently handicap the matchmaker when trying to create balanced matches. Where a more balanced match would have existed by splitting two good players onto each team, it forces the matchmaker to put them together on one team. This would not be as much of a problem if the population weren't so low that the matchmaker can rarely find another good duo to balance out the teams. So when two 1700+ rating players duo queue together and the queue has gone on for 5, 6, 7 minutes+, the matchmaker can do nothing but put them together with three 1400 rating players against a team of five 1400 rating players (just an example, but generally what happens). Yes, if you're one of those people crying about going against MAT winners in your gold match that ended up 500-0, this is exactly what happened.
2. What's worse, even semi-good players will start queue dodging when they know a duo of good players is queuing. Say we have a plat 1500 player - he knows that a duo of 1700 streamers are queuing. The 1500 player will more often than not choose not to queue at the same time because the odds are he'll be placed against said 1700 duo and have no chance of winning. He would be MUCH more likely to queue if it were solo-queue only because he then knows the two 1700 players would be on separate teams and he'd have a chance to make an impact on either team. This throws the match quality further off for everyone.
3. Even more nefarious, there are some players who will abuse duo queue to get favorable games. The matchmaker looks at a duo and takes the AVERAGE of their rating when putting together teams. So two top players can take advantage of this by having one player get on an alt account that is much lower rated and so they get better players on their team. Some will even go out of their way to abuse this by throwing games on the alt account to keep its rating low, so that they can keep boosting their main account.
All of these things absolutely happen with every ranked season, and anyone denying this is an absolute liar.
And yes, I've been around long enough to know the history of how duo-queue was allowed to stay because top players wanted to play with their friends.
Anet should pay attention though because the things above lead to a vicious cycle that causes the experience to become ever worse for the general population. Again, none of these problems would be so bad or exploitable if the population was even somewhat higher. But CMC or whoever, the population is so low now that you really have to re-evaluate.