That relies on the front fork being at an angle, though, doesn't it? If they made it straight down (which is the obvious choice) or pointing backwards, it would be much, much harder to ride.

Bicycles actually are less stable with a more angled fork. If the fork was perpendicular to the ground it would be very difficult to turn.

the geometry of the ride type of a bicycle or motorcycle is really interesting [1]

[1] https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometr...

Maybe in spherical cow land, but in the real world bicycles don't get very far without a human to maintain balance. It would fall over the first time it had to ride over a piece of debris on the road.

Objectively not true. Here’s a video of a unmanned bike rolling over a curb without any trouble: https://youtu.be/oZAc5t2lkvo?t=145s

Stuff on the road will only knock the bike over if it stops the motion of the bike first. The need for motive power was already acknowledged.