Yeh- I've got this a bit wrong !!!

In the Octy3, there's no light on dash to indicate the headlights are on - only on the actual light switch itself.

But there ARE lights for front & rear fogs, and high-beam. Which is all fine I guess, IF they dimmed with the rest of the dash lights.
Interestingly, the Kia Cerato hire car I'm currently in, it dims ALL dash lights - even the head/fog/highbeam lights, which would definitely be the preference to reduce distraction.

Curious to people's opinions - is there an engineering reason why cars don't just have their lights on all the time?

All my previous cars, I've driven with the headlights on ALL the time. I was taught this way, so that I'm visible to other drivers more easily.
Laws in Australia were made so that motorbikes must have their headlight on when ignition is on, for the same reason. I remember there was a lot of angriness when this law was first introduced, as riders had to get their existing bikes rewired to do this with the ignition circuit, but now, it's just normal to see bikes with (at least one) headlight on all the time.

So why do people object to doing this in cars?
If lights just came on automatically when starting car, there would be no reason to even have a light switch, never mind an "auto" switch or light sensor, or distracting bulbs in the dash reminding you the lights were on....

Is this a personal preference thing for drivers to NOT want lights on at all times?
Or a valid engineering reason for it (reduced lifespan of bulbs etc..... but that's a redundant cost when compared to an accident or loss-of-life)