Hi @Mikenux!
Basically for the same reasons pointed out years ago by other users in Workspaces in grid (#1560) on Gitlab. In a nutshell, it is way more efficient and user-friendly when you use several workspaces (I’d dare say more than 3).
Fewer steps: Compare a 3x3 grid with a 9 linear layout (vertical or horizontal). If you wrap your workspaces, with the grid you are within 2 strokes from the furthest workspace (say, Down then Right) compared to up to 4 in a linear layout (from workspace 2 to 6 or 7). If they are not wrapped, the difference is between 4 and 8 from the furthest workspace. For the same reason, it is also faster to move apps from one workspace to another using keyboard shortcuts in a grid than through the activities overview.
Mnemonics: It’s much easier to remember where you and your apps are. Compare “I am in the Centre and Thunderbird is in the Upper Left corner” with “I am in Workspace 2 and Thunderbird is in Workspace 7”.