Complexity. Adding a starter completely changes the car. I mean completely. Ewsca used to have starter clutch cars. Super winged modified. They were big and heavy. #1 issue is there's no space to put a battery on these cars. Much less add a clutch and change the rear suspension.
Here's another thing about refusing to change. They won't make the cage 3" taller to save a drivers life it a top impact because of weight. Your talking 2-3lbs.
Why the heck would they want to add over 40 between clutch battery starter and all the other changes.
Plus do you realise how hard it is to turn over a 14.5:1 compression engine that's cold and has a fuel that doesn't burn when it's 50* out in spring fall. That's a big battery and and big starter