Fuel Line Question

Just wondering ,,,, why doesn't karters use rubber automotive fuel line for clone motors , as opposed to the clear / colored vinyl fuel line ? Converting from flathead to clone and just questioned why .
I use the clear line because I can see any bubbles if they are there, Bubbles to me says that air is getting in some how, and I sure don't want any extra air inside my Dual Buller billet carbs on my Sudam stroker at 14,500rpm's.