There are a few wealthy PhD students even at the topflight PhD programs who are doing it “for fun” without concern for employabilitly.
One case mentioned by an elite U prof I had for a summer class in his/her department is a member of a family well-known for their wealth and political connections. I also met a few who were scions of foreign wealthy/political/aristocratic families at another elite college where I took some graduate classes.
They are full-pay, subjected to lowered admission standards as a result, and given far less support/mentoring by many topflight advisors who prioritize PhD students with fellowships who are viewed as the best prospects to continue the department’s reputation for producing productive topflight scholars in academia and to a lesser extent related non-academic jobs.
Another group who aren’t concerned about employability are those who are going into PhD programs because they are doing it as part of their jobs and thus, continue to have salary/benefits through their employer such as private industry/government departments here in the US/abroad send their chosen employees and defray the costs of the PhD program themselves.
Some examples I can think of in this category are a few grad classmates who were sent by their their respective military services to start PhD programs so they have the qualifications to start their 3-year tour as FSA instructors, a few selected international grad students sent by foreign governments to pursue PhDs to facilitate their moving into research positions required for their career tracks, or private industry sending their employees to pursue PhDs related to advancing in their industry career tracks(mainly in sciences such as chemistry or engineering/CS).