When the materials and manufacturing options (MMO) are dodgy and limited, you have to come up with almost a perfect design to take advantage of what's available

When the materials and manufacturing options (MMO) are dodgy and limited, you have to come up with almost a perfect design to take advantage of what's available. There's less room for error. When MMO got better, you could get a lot "wrong" and still have a useful device. In other words, early on you have two obstacles: MMO and finding a good enough design. As time goes on and MMO improves you only have one obstacle: design, meaning progress is faster or at least shows enough promise to motivate further experiments.