@TaxGuyBill Blind people trying to describe an elephant.  All I see in the question is a working couple with kids who are trying to qualify for loan forgiveness by filing separately.  I have had clients in that situation, working in government or nonprofit jobs for which Congress has said, "put in 10 years and we'll pay off your loans if you keep your income below a certain level."  And Congress, probably not realizing what it was doing, said (or told the bureaucrats to write regulations that said) "we look only at your income, if you file separately, but at your joint income, if you file jointly."  

Other people may be looking to qualify for new loans, or defer paying off old ones, based on other programs and other laws.  But you're right, these (probably) teachers aren't being "forced" to file separately.  They can always file jointly and pay off $50,000 or more in loans that otherwise they have been promised will be forgiven because of the low-paying jobs they weren't "forced" to accept.