I think there is a confusion going on there. Should reflect to what is ethical, what would be the best option, and I don't see how the manufacturer’s interests really matter for that. Self-driving cars should cooperate with each other in various prisoner's dilemma, not defect with each other, and more generally, they should behave in a way to smooth traffic globally (which at the end of the year would lead to less traffic time for everyone if all cars do so), not behave selfishly and minimize the passenger's travel time.

Now, in a competitive market, due to manufacturer's interests, it is indeed unlikely they would do so. But that is different from should. That's a case of pure market leading to a suboptimal solution (as often with Nash equilibrium), but there might be ways to fix it, either from manufacturers negotiating with each others outside the market channel to implement more globally efficient algorithms (like many standard bodies do), or through the state imposing it to them (like EU imposing the same charger for all cell phones).

Of course there are drawbacks and potential pitfall with all those solutions, but that's a different matter than the should issue.

What if a company makes a large number of cars? Would they make cars that minimize travel time for their occupants, or for all people who buy cars from that company? Would multiple companies band together, and make cars that minimize travel time for everyone who buys cars from any of those companies?