It sounds like you basically dropped all other costs but teacher salary and found STEM professor salaries to be 10% higher
(Facilities dropped, same cost per student on dorms + maintenance, building capex dropped)
You really need to do a per-student cost analysis - e.g. if there are 500 STEM graduates and 2000 liberal arts, the costs are not evenly spread across the non-academic staff, and you need to account for the separate facility costs (e.g. a computer/science lab is much more expensive to maintain and stock than an english classroom)
And There are also lots of intangibles to factor in -
-How many of the alumni contributing to the endowment and paying for academic buildings are STEM vs. liberal arts graduates
-How do graduation rates and job outcomes differ between STEM vs. liberal arts, and affect the college's KPIs (e.g. 95% graduate on time and 80% get a job within 6 months making a median $70k, for marketing)
Also presumably your school has an endowment and investment managers, which is the largest source of revenue for top tier schools (Yale's endowment of $27.2B returned 12.3% in 2018, the school spent $1.4B of that return on operating costs making up 34% of the university's net revenues [0])
So really in the grand scheme of things, most major universities are safe investment vehicles that are (1) extremely marketable to wealthy alumni (2) have great information networks and (3) generally enjoy major appreciation on their real estate value, making the comparison of STEM vs. liberal arts salaries pretty negligible
[0] https://news.yale.edu/2018/10/01/investment-return-123-bring...