1) It's way faster and easier to rout the t-molding slots if the parts are convex. Then I can use the router table instead of having to run a hand held router around the parts. Takes literally 30 seconds to do all the pieces on the router table and it's a lot safer.
2)Since the control panel is a separate part, it's easier to wire and set up and I can make it wider.
3) Since the monitor section and the control panel are separate pieces, I can swap out control panels with different configurations.
4) Also, it's easier to mount the monitor since I can lay the bezel section flat on the table and let gravity hold the monitor down while I attach it directly to the wooden bezel.
I've done some the other way too...