I think the answer must be that some do, but different forces like cost and fashion intervene in other cases. Take, for instance, Conklin’s crescent filler. This was an undoubted improvement over the eyedropper filler, in that it was self-contained and efficient. That its utility was appreciated is shown by its longevity – from the last years of the nineteenth century to the early nineteen thirties. During most of that period it was competing successfully against the lever filler. In the end, though, the crescent filler died and the lever filler triumphed. This may, at the margins, have been influenced by production cost, but I think it was mostly fashion, in the sense that the protruding hump of the filler began to be seen as clunky and old-fashioned.
Another early filling system, De La Rue’s Onoto plunger-filler, pre-dated and competed against the lever filler in a similar way. It lasted much longer, until 1955 in the UK and a few years longer in Australia. I have seen it asserted that production of the plunger-filler ceased because the filling system had become outdated, but I don’t think there’s any truth in that, or at least not in the normal sense. The reality, I believe, is that the shrinking market for fountain pens caused De La Rue to try to find a way of reducing production costs. Manufacture of the K-Series piston-fill Onotos was subcontracted to a German firm which had much more modern machinery and could achieve large productivity savings. Only final assembly was done in Britain. De La Rue was not alone in using this solution. Later, Conway Stewart would follow the same route. One might say, then, that the high production costs of the plunger-filler became outdated, but not that the system failed from inefficiency or unpopularity. It was, and remains, one of the most popular and effective filling systems – the high price of restored Onotos is evidence enough.
There are some filling systems that became largely rejected by the industry. The blow-filler, an inelegant and inefficient method, had a short life, its only real benefit being the low cost of production. Syringe and bulb filling are almost in the same category, but not quite. Neither is intrinsically a bad method, though one might say that the syringe filler lacks elegance as a solution. Nonetheless, it’s the basis of many converters today. The bulb filler, with a breather tube, is a highly efficient way of getting a lot of ink into a pen. The problem for these filling systems was that they were cheap to implement and were taken up by companies selling pens at the bottom of the market. Often poorly made, they led to customer dissatisfaction that, a little unjustly, caused to these systems to be rejected.
What about the lever-filler? Did it become outdated? In truth, I think it did, though its demise was from several causes. By 1960 or so, the fountain pen itself was no longer the first choice of writing instrument. Led by Waterman, pen companies saw an opportunity to salvage profitability by producing pens that would accept only a cartridge made by them, a modern marketing concept that had been pioneered by Gillette with its safety razors and continues today with inkjet printers. A pen with no moving parts was cheaper to make, too, and so the lever filler faded away, the end of a very long tale.