Not none, but very few in the stem fields (less than 40% from my estimates).

Why would you pursue a PhD with a 25k/year stipend when you can just start a near 6-figure job and start paying off your student debt?

Only the ones with financial freedom or commitment to research take the PhD pill. Or when you go through a recession and you want to delay the entry to the job searching market.

This is exactly the problem with the system. If there are tons of foreigners willing to get grad degrees and work for a small salary increase over a bachelor’s, US students are not sufficiently incentivized to do graduate studies.

The percentage gets worse when you look at the top say 10% of PhD students. Go to AI/ML conferences and see who is presenting the papers; it’s almost all international students in US universities or students from outside the US.