Those programs are different for the following reasons:
- They're pre-professionally oriented and targeted towards their prospective students as such unlike academic PhDs(including STEM).
- They often have lower research requirements compared to their academic PhD program counterparts due to the pre-professional orientation and part-time status.
- Unlike the academic PhD programs, the pre-professionally oriented PhD programs you're referencing are viable because they may actually serve as viable cash cows for the university as many of the part-time PhD students' studies are likely being mostly/completely funded by their public sector employers....not from the universities through fellowships.
In that respect, it’s no different from many pre-professional Masters programs like MBAs or professional Masters programs like the ones some relatives/friends earned part-time while working for their employers or in one case, as a “thank you” for being a good organizational business consultant associate for 2 years*.
- One perk BCG and other organizational business consulting firms offer to associates who completed 2 years right after undergrad successfully is full funding to any graduate program the successful associate is able to qualify for admission. This was how one in-law managed to earn a top-3 MBA while having it completely funded by one such firm after completing her 2 year associate stint there.