It could have advantages - you're right. But there are two fundamental point that you continually miss. Firstly, for your dream to come true, it would take ALL manufactures to have the SAME vision, which given that they compete with each other, not collaborate with each other, it's never going to happen. Secondly, whether you accept it or not, by default, it limits creativity and design possibilities.
Personally I do not wish to live in a world where everything I buy conforms to per-determined specifications. I choose to live in a democratic western world, where free choice is available, and long may it continue. If you wish to adopt a utilitarian approach to your pen making, you go right ahead, and I will even give you some pointers. Sierras and their many variants all use the same bushes and drills. Barons and sedonas and their clones all use the same bushes and drills. Churchills and statesmen use the same bushes and drills. Jr Gents and their closes all use the same bushes and drills. There are others too. In the main they are all extremely dated designs, made in their day to a uniform standard of sizing within their groups, and the world of pen making has moved on considerably since.
