From the Patch Notes:
Developer Notes: The change here is to better manage our player community without splitting them between too many playlists at once. The goal is also to give a clearer game mode option for our more competitive players while also providing the Arcade area for those looking for less pressure in their experience.
The dev team learned that with the current size of the playerbase, it does more harm to try to run Squads + Solos + LTM. While I myself really enjoy Solos and played Solos 80% of the time, it is an understandable change given the fact the team is trying to make sure players are not spread too thin.