The lobby just has to show all open lobbies and you should add filters to make a selection. One of the possible selection just be the game mode ‘death match’. Then it select all rooms in the lobby with DM selected. That sounds pretty easy to create.
Its not a design, its something beyond what the game can do or too troublesome for what they think its worth.
Lets remember that right now, since crossplay with Xbox, and back last year when ranked lobbies were created (it had horrible lagging to the point DMers barely cared to play the PUP, that was already plagued), the game started to have some odd instability
Well, Im just telling you what I know from trustable sources. Dont believe it or complain with them about this being available in HD.
There’s a DM discord with most active ranked players, its the easiest way to find games or someone to play with