I would argue it's both: Yes, there are more scientists than ever but the scientific landscape has also become considerably larger. Everyone is doing research i

I would argue it's both: Yes, there are more scientists than ever but the scientific landscape has also become considerably larger. Everyone is doing research in a different niche and every niche occupies maybe 5-10 people. Also, no one knows all fields or research anymore. So any sort of breakthrough will take time. And we probably did have a lucky run in the sense that the phenomena in fundamental physics are comparatively simple – at some point you will have solved them. They are not nearly as complex as phenomena in condensed matter, for example, where there might be some overarching patterns & schemes, but ultimately every material is still going to be slightly different and come with unexpected (or at least very material-specific) properties. (The recent discovery of the room-temperature superconductor might be a prime example here.) The thing with complexity is, well, that it's complex. Why are you expecting any general breakthroughs?