From my memory of the time, I think it was a few things.

The ability to do 3d in games was new, and without a lot of experience in what made for “good gameplay” devs were trying new things and seeing what works. Similarly, if you go back even further into console and PC gaming history you can find some game that use what, looking back, would be considered terrible control layout and/or gameplay mechanics. Sometimes because the company just wanted to ship something, sometimes because best practices hadn’t been established.

The ability to do 3d was new and the free roaming camera was an easy way to show off the systems capabilities. Especially for early first party games, there was a huge effort to show off how much more advanced the new console was compared to the competition. I can remember marketing that focused on showing that you could look all around these virtual worlds (Mario 64) or how awesome the graphics processor was by highlighting the parralax effect of the background images (Castlvania 4).

Controllers were also evolving at this time. The SNES and original PlayStation controllers just had a D-pad and like a half dozen buttons to control all your movement and actions. The addition of analog control sticks, and the N64’s bizarre controller were really the first shot at having the variety and quantity of controls to make rapid changes of player perspective and actions feasible at the same time.

Combine all of that with some publishers just putting out blatant cash grabs, and you have a whole lot of new territory to map and a target audience that doesn’t really even know what it wants yet.