Once you down that route - or any 'compulsory' requirements - you open a whole can of worms: design regulations (for separation of fuel systems, minimum size of auxiliary, etc.,), yearly tests / inspections, etc.,. And this regulatory behemoth would all have to be paid for...
I'm sure we'd all like to carry auxiliaries, etc., but in reality can't and have to balance risks.
"Can ye model it? For if ye can, ye understand it, and if ye canna, ye dinna!" - Lord kelvin