1. The rate of meaningful new discoveries in basic research has slowed significantly compared to the mid 1900s. Most important advances now involve enormous groups of researchers, and require decades of work. So the basic research route is less appealing overall.
2. Technology and finance provide clear avenues for outsized financial returns that simply weren't available in the past. Enrico Fermi, for example, was fairly enterprising. He wasn't an academic ascetic at least, and made some effort to amass wealth. But the best strategies he came up with were publishing textbooks and maybe some dabbling in the stock market (That is if I remember my details from The Last Man Who Knew Everything [2] correctly)
[1]: https://www.goodreads.com/book/show/11797471-the-idea-factor...
[2]: https://www.goodreads.com/book/show/34746094-the-last-man-wh...