It's a simple question that doesn't have a simple answer.
The answer is 'mechs' because they are regulated by resistance.
It's because people started drilling holes in tanks to have more airflow, are more air needs more vapour to 'balance' the vape.
It's because people wanted bigger clouds and needed more airflow.
It's what
@oldhippydude said (and he's probably as cynical as me) ... how can a company sell you a 200w device when you only need 10w?
It's all these things and more.
There's no doubt that thin high resistance coils work, I'm always blown away by the performance of my naturevape coils, which are tiny micro coils made of thin wire 1.8ohms and at 7 or 8 watts produce better flavour and vapour than a 0.7 ohm nautilus coil.
People like to make massive generalisations about coil resistance but on regulated devices it doesn't make as much difference as you'd think. A 1.8ohm nautilus coil really isn't that different to a 0.7 ohm nautilus coil to vape on even though it's a huge difference in resistance. Why? because it's fitted in the same tank with the same airflow, same sized chimney and fitted in the same coil head and you just adjust the power so it vapes how you like it.
Those 0.2 smok coils that run at 150w? (or whatever) ... there's no doubt in my mind that you could make the same thing with a higher resistance that would need less power and vape just as well if not better. But for that company in particular that whole high power thing is a selling point now.
..... also there's almost no difference between a 0.9ohm coil and a 1.1ohm coil on a regulated device, but one is 'sub-ohm' (and all the connotations that come with that) and one isn't (and comes with another load of connotations) but in reality you'd be hard pushed to tell any difference on a regulated mod with the power adjusted accordingly.
...or maybe I'm just talking a load of nonsense as people seem to have different experiences with different gear, we do all vape differently..