It was a purely financial decision, they've completely disregarded the health of their students and prioritised the financials.
I remember when I went to Uni the first few weeks were critical, to get a feel for your new home and area, get to know your peers, forge friendships, go out and have some fun, enjoy some drinks at the local pubs and clubs, all that stuff that young people want to do, all the stuff they need to do.
What a fucking miserable position they've been put into, shelling out £127 per week on rent, on the hook for £9250 in tuition fees for just one year, most of their learning is going to be remote anyway, they can't go out, they can't socialise, and they've been told they'll be breaking the law if they decide they can't tolerate it and want to go back to live with their parents.
As per the article I've linked there, in some of these halls they can't even control the temperature of their own room, the rooms are small, the beds aren't the best etc.
Make no mistake the bigwigs in charge absolutely knew that the halls of residence would end up as human petri dishes and this is the situation they'd end up in, but they wanted the money more than they cared for the wellbeing of their students.