I think because cars, although primarily a form of transport, are often also a fashion accessory, or a statement of who you are (or aspire to be). And touchscreens are very fashionable[1].

Cameras aren't really like that. Nowadays if you've actually bought a camera as opposed to just using the one in your phone you're probably at least a little bit into photography, and in that context the function matters more than the form and style.

[1] I'll grant that cost, along with simplicity of reconfiguration via software, may also be factors.