Because it is an investment in the betterment of society, and here is the part that you'll like best: helping people pay for higher education helps to break the cycle of intergenerational poverty, so that people who might otherwise have ended up dependent on lifetime entitlements turn into self-sufficient taxpayers.
Most of the people who are targeted for this possible forgiveness program are people who were taken advantage of by unscrupulous for-profit educational institutions that charged them way more than the program was worth in terms of earning power, leaving them now among the working poor, and sinking deeper into debt by the day because of the compounding interest.