Local economies, especially college towns and cities, depend heavily on the business brought by college students in the area. Restaurants and bars will be especially hard hit if students don't return for the fall semester.
This not only impacts the economy on a financial level. Many of these businesses which depended on college students will be forced to lay off employees as business dwindles in order to keep running costs low. People's livelihoods are at stake if the bulk of their consumers don't return. In some big college towns, students from multiple colleges and universities make up over half of the town residents.
Students rent properties, buy food and drinks, go shopping – without this kind of cash flowing through the towns and cities, all manner of businesses will be negatively affected. Only approximately 23% of colleges and universities in the US will be returning for primarily in-person classes, while over a third will be mostly online or hybrid platforms. 
College towns and cities depend on the academic year (September - May) for the bulk of their revenues. Without this source of income, college towns, especially small rural ones, face total economic collapse as their primary source of income does not return.
These economies have been build around the colleges and universities and were doing well – attracting businesses and generating employment and town revenues – up until March when students were sent home.
College/university students are vital components of many towns and cities and key drivers of local economies. To keep these students away risks destroying local economies which will in turn lead to ever wider economic fall out as cash flows dry up and money stops circulating in these towns and cities.