That's still 3-6 fewer miles worth of charging to do from more expensive sources. Even if it can't come close to covering your full use it's still covering something

Not if it won't recover it's own costs.

Cost is convenience.

Manufacturing cost is like $40 cells, $20 electronics and $200 in glass fusion, mounting, etc.

My car eats 200W just being online so it would be useless to charge from solar.

It may still lose on this, but you would also want to include the externality costs that the consumer doesn't themselves bear for whether it is worth it overall.