It's a balance of performance, appeal and price also. Solar surely cannot power a car that is very powerful and power hungry. Battery tech used to be pretty crap too, but phones get more powerful, screens get bigger and batteries are improved as demanded (it got better for sure). Of course batteries in phones is crucial, solar panels on cars or anywhere else is not. And more and more people nowadays are saying Nuclear is the only true clean reliable power, so I feel solar panel progress isn't going to be pushed as hard as needed. Tesla's own solar roof tiles, previewed a few years ago, is not yet in the marketplace, and Walmart is suing Tesla for gross negligence over their (regular) solar panels causing roof fires. You're right, solar tech is not as good as it needs to be and not sure it's going anywhere right now.