Part of it was that keybindings were still in flux at the time. Strafe actually appeared in Wolfenstein 3D already, but the way you did it was by holding Alt while pressing left/right arrow; you used the arrows without Alt to turn around (and using the mouse to turn was very uncommon back then). The original Doom inherited that.
It wasn't really a good setup even in Wolf3D, but it took some time for the gamers to figure that out, and for those findings to percolate as the defaults in newer games. Even Quake (1) didn't have mouse look + WASD enabled by default. I think part of the inertia was that arrow keys were so ingrained as navigation by design (they're arrows!) that abandoning them just didn't make sense.
It wasn't really a good setup even in Wolf3D, but it took some time for the gamers to figure that out, and for those findings to percolate as the defaults in newer games. Even Quake (1) didn't have mouse look + WASD enabled by default. I think part of the inertia was that arrow keys were so ingrained as navigation by design (they're arrows!) that abandoning them just didn't make sense.