The early workstations like the Alto, PERQ, and CADR were portrait by default, and used specialized CRTs.
Personal computers tended to use 4:3 displays because they started out with either terminals (which used television CRTs) or by being plugged into literal televisions.
Workstations went to two-page displays a decade and change before even 1024×768 was widespread for personal computers outside ones used as workstations (e.g. very high end PCs and Macs used for CAD, page layout, etc.).
Personal computers tended to use 4:3 displays because they started out with either terminals (which used television CRTs) or by being plugged into literal televisions.
Workstations went to two-page displays a decade and change before even 1024×768 was widespread for personal computers outside ones used as workstations (e.g. very high end PCs and Macs used for CAD, page layout, etc.).