It was new technology, 3D was a fairly new concept in gaming in the mid 90s. But it took so long to get properly implemented. You have super mario 64, gex enter the gecko, lemmings 3D. I am wondering if it was a business decision and not the devs who pushed for a free roaming camera, since it was clearly not a satisfactory result gameplay wise. Because at the same era, you have games with fixed camera angles that are much better experiences overall.
I played OG Doom for years with keyboard only. Up/Down arrow for forward/backwards, Left/Right to turn, and then holding Alt to strafe. RIght hand on the arrow keys and left hand controlling strafe/run/weapon selection.
I don't honestly recall if mouselook was even an option back then, but I tried playing with those keyboard only controls recently and literally could not even. It's kinda wild how hard it is to imagine anything other than WASD-mouse for a FPS these days.