Importance of campus for mathematicians
My degree (pure math) is from long ago and almost all my work was done working alone, though I had an office at the U. There were two exceptions. One was that the coffee lounge was both a good place for a break and a good place to bounce ideas around. The second was that we had a periodic seminar of a few faculty and students interested in the specific research area.
But both of these (other than someone else making coffee) are doable in the modern world with internet connections. There is no reason to give up the &quot;contact&quot; with others if you have access to email and zoom. Even the seminar environment can be replicated effectively.
One issue for some is the possible distractions of having family around as you work. I had two children by the time I finished, so working at home (pre internet) would have been pretty difficult, even though the work I did was mostly in my own head and not collaborative.

I suspect that in applied math, closer contact with colleagues is more important than in pure, but I don't have experience with that.
But, the world is as it is. We all need to learn better ways to cope with that.