Mind sharing why? I think I can guess: the potential for disaster with a heuge amount of ink stored in that barrel?
Before the "self-filling" fountain pen, eyedropper and dip pens were the norm Today, I don't have to deal with the threat of an ink
burp, or the pocket full of ink. I like the additional layer of defense (sac, cartridge, etc.) against ink. The large capacity is not an
attraction, since I am never far from my ink. It takes a long time to use three or four milli-litres of ink. Also, I enjoy the ritual of
filling my pen. I do, however, appreciate all those who have taught me how the conversion is done. Thanks.
Of course, piston fillers are simply cool ! And, if I ever come across a Parker "Trench Pen" that is not tied down . . . . . . .
So, the short reasons are serendipity and cowardice.