> To see this, here’s an exercise you can do yourself, if you have any training at all in advanced mathematics. Take a fairly generalist journal, like the Journal of Algebra (take a topic in which you have expertise — my doctoral thesis was in algebra). Look at some of the papers. How many of them are truly interesting to you?

> These days, I can look at any of these journals and find at most one or two papers that are even remotely amusing, and algebra was my specialty. On the other hand, I can take a journal in biology like the Journal of Animal Behavior and still find quite a few papers in each journal that are interesting to me even though I’m not even a research biologist! Keep in mind I still like mathematics a lot, and I still enjoy algebra.

Can't you also say this is directly disproving his point as well? It might be that there are so many open interesting problems that we can become highly picky what problems get solved to the point these preferences are shares between less people. Indicating an expansive set of problems instead of an exhausted one instead.