King’s Row is most likely the most popular map in the game by a fair margin.
However, as the game now has roughly 20 maps in the rotation you don’t get to play it very often outside of custom games. (If the maps are used evenly you only end up on Kings Row around 5% of the time)
Putting it in a separate area would allow the players that want to play it more to easily do so and would allow the few that hate the wonders of Kings Row to never play it.
2CP is probably the most hated mode in Overwatch and if the maps are selected evenly, people are stuck on it around 20% of the time. However, probably somewhere between 10% and 15% like it the best of any mode.
Putting it in a separate area would allow the players that want to play it to do so and those that don’t the ability to not do so.
You’d want to use a separate area so that it did not eat up Arcade slots and so that it would not be warped by Arcade’s lootbox incentive. Unless you are absolutely desperate for players having people coming to a section for rewards has a high chance to damage the section.
With all that said, this approach would have guaranteed downsides and potential downsides.
The queue times for Quick Play, King’s Row, and 2CP would be longer than they are on live in Quick Play.
The change will move a fraction of Quick Play’s population out of the mode which will raise the queues times for Quick Play.
King’s Row and 2CP will only have a fraction of the players Quick Play does and thus take longer to queue.
People can go for too much of a thing and burn out.
It’s entirely possible players might dive into the modes play them too much then not want to play them again.
Putting it in a separate mode can change how it plays for the worse.
You’ll have an audience that doesn’t match what Quick Play has currently and that can lead to worse results.
Players that play the mode repeatedly might gradually create a culture or a minmaxed meta that is unappealing.