Machining trit slots is a no win choice for any manufacturer, large or small. It seems that half the flashlight buyers want slots & the rest want no slots. Any maker is hesitant to include a feature that will cost sales & they are also reluctant to stock or make excess inventory so that the necessary light is always in stock.
The most economical time for slot milling is when the light is fixtured in the machining center. Adding one tool change (to an end mill) and including a few additional lines of program code are not costly. The major cost is in the extra time needed to machine each slot. Even the smallest 1.5x5mm vial requires at least seven back & forth machining passes in aluminum to reach full depth. Titanium 6-4 is even more time consuming as it takes fourteen passes & each pass takes twice as long. Multiply the extra time per slot by (for instance) half a dozen slots in the rear & half a dozen slots in the front & the cost of that light just went up, reducing overall sales.
Having slots custom milled gives the owner choice of total number, location, pattern, size, color, etc. It allows your light to be totally different than the identical model owned by a friend. Slotting isn't inexpensive because of the large investment in specialized tooling & because of the time required but it gives the owner exactly what they want. As long as there's enough thickness to work with the slots can go in some interesting places. The photos below are my C2 that stays in the nightstand drawer & it is certainly easy to find