Unfortunately, dynamic queue has had a fair number of issues – ranging from elongated queue times, especially in higher ELOs, and unfair matchmaking. For example, solo players have often been the ones getting put into unfair situations where they are forced to play against coordinated groups of people because of the algorithm behind dynamic queue.
Here is an excerpt from the official website announcement that suggests solo queue will not be returning:
Afterwards, he goes on to say that:
Bad news for all you lone wolves out there. Personally, I hope Riot can find a way to make both solo queue and dynamic queue work, because it is not fair to hang people who prefer to play alone out to dry when playing solo currently leaves you with an inherent disadvantage.