It's because it's considered settling for lesser to "sell out to industry."
Kinda reminds me of the old "amateur athlete" paradigm.
It's not that you can't get a good job with a math PhD, it's that you can't get a good job and the respect of your peers/community. I'm sure there are plenty of companies that would be thrilled to hire math PhDs, they just don't also offer a ton of opportunities to work on cutting edge (math) research and publish papers.
Kinda reminds me of the old "amateur athlete" paradigm.
It's not that you can't get a good job with a math PhD, it's that you can't get a good job and the respect of your peers/community. I'm sure there are plenty of companies that would be thrilled to hire math PhDs, they just don't also offer a ton of opportunities to work on cutting edge (math) research and publish papers.