They exist. It’s the one and only reason I use Linux is I fell in love with i3 and now Sway.
They’re not just good for terminals. I do like me some tmux but I find tiling and stacking and all the glory of a titling window manager the best part of desktop
Linux.
I would say those aren't really desktop environments. They provide the bare minimum for window management and compositing, but not much more. Desktop environments encompass much more than that, like managing file type associations, and protocol handling.
They’re not just good for terminals. I do like me some tmux but I find tiling and stacking and all the glory of a titling window manager the best part of desktop Linux.