Why does surefire use twist-on tailcaps?

It's bothered me for a while. A lot of the models they offer are press for on, twist for constant on. It looks like in order to get a tailcap that allows light press for on, and full click for constant on, you have to spend more. Do they really cost more to manufacture?

the twist-constant-on lights are intended for use in tactical situations where going for constant on should be a deliberate action, not an accidental action.
if, in the heat of battle, you briefly push your momentary-only pushbutton, yes, you get a flash of light but no more, whereas with a clicky you get light that stays on until you turn it off manually, not a desirable feature.

SureFire lights designed for use primarily outside tactical situations, like their Executive-Series will come with clicky switches instead.

Also because a twisty tail is easier to operate than a twistie head (i.e. the Surefire "C" or Surefire "Six"). Cypher Aod kinda hit on it a bit, but it also acts as a "Dead-Mans switch" for your flashlight.

Also it is very reliable and easy to clean. If the internals of a clicky stops working you need to wait for a new part from customer service.

Although seldom mentioned and surely no real reason - but with a quality twisty like the Z41 (in other words - not the Solarforce S7) you can adjust the length the switch has to travel for activation. Screwed on short before constant on and you have a short "trigger" way for e.g. strobing your light. Or screw it down just until it first lits when depressed - longer trigger way, more secure against an accidental discharge of light.

Cheers
Thorsten

Another reason is sheer simplicity, it's one piece of metal touching another piece of metal, there's less to fail.

I also like the quiet operation. A Twisty tailcap can be operated without any click sound. It's a tactical feature, but the 'click' of my Fenix LD20 can wake up my daughter, if I am very near; the twistcap of my Kroma does not.

I'm not an experienced Surefire user, I just got a 6P and a G2X pro a couple of days ago.
I also have a C2 since a few month back.

The twist tailcap was very reliable what I had heard but seemed a little awkward to use. That was what kept me from buying my first Surefire.

When I got my C2 I realized that it worked very well in an overhand grip. Now with my 6P I realize that it also works very well in an underhand grip.
It feels totally natural and easy to hold the tailcap with my 4th finger and twist the body with my indexfinger and thumb.

So, it's an on/off system that works very well in both underhand and overhand grip.
If you want to hold a flashlight with an ordinary tailclicky in an underhand grip you need to change grip to switch on/off.