This is I’d say partially because we don’t have a HUD that can handle the bandwidth and pace of data required for rally. Overlaying a visualization of the turns ahead would be much better than a copilot for sure

If we have HUDs that can handle aerial combat, why don't we have HUDs that can handle racing?

Budget? It's a better trade-off to have a second human and to put the money into tuning the car.

this is true, so we just lack the incentives to make them? a human copilot is just a core part of the sport?

It will be fun when we get to the era where this is bulletproof-reliable to this extent, but for now, recorded notes with accelerometer-backed GPS locations are probably a better idea than hoping the AI will be able to do this for you dynamically without you driving off a cliff.