I did place gas stations all over the city (using Find It), spreading them out so it makes sense to cover all areas. Something I had neglected to do because I assumed the game would do that on its own. Hopefully that will encourage car ownership now! They seem like popular destinations for the cims!
Now, I was going to encourage such buildings to spawn naturally by
lowering the Commercial tax rate for Petrochemicals, but that category is missing as a choice(!?) so we can't do that! We can only do it with the industry version of the taxes but that won't encourage Commercial buildings to spawn. So, I think that is a bug/oversight and hopefully the devs will enable that tax rate in the game ASAP! Can't be that hard to get in there, like 30 seconds