The physical design of FireWire was one of its many advantages, in that you could instantly tell, visually and by touch, which side was up by the beveled corners on one side of the plug. I’m guessing the answer here was again cost, that manufacturing an interconnect with two 90-degree angles and four 45-degree angles was more expensive than one with four 90-degree angles, but I’ve never seen any confirmation of this.
The sole reason as stated by Ajay Bhatt, the project lead at Intel, was cost. They wanted to encourage mass adoption of USB and every cent saved helped in that initiative.
The compromise for UX was to make the connector rectangular rather than circular, so that there was a 50% chance of getting it correctly orientated on first try.
I never ended up getting a camera or anything else that supported FW, but USB always seemed to work well enough for my (relatively light) use case.
Meanwhile we were connecting printers, scanners, and other peripherals using a 25-pin parallel (or sometimes SCSI) plug. Granted, the DB-25 was already pretty old at that point, but I have to imagine a 24-pin reversible USB plug would have been close to that size if it had been developed in the 90s.