film techniques - Why are most scenes in a car recorded with chroma?

Of course this changes from country to country, but generally speaking it's not illegal to film on the streets, since it's a public area.

Most car scenes are recorded with chroma just for pratical reasons.

In a professional production you look for "quality" and you can achieve it only if you have control. It's all about control.

With a studio setting you get full control of the lights, the movements, etc. in one word, the scene. And of course, you minimize the hitches that can occurs in the real world (also safety concers).

However you should film outdoor shots to enrich and give credibility to your scene.