Sympathy is not a finite resource. It is perfectly possible to by sympathetic to victims of crime and also sympathetic to people who are suffering more than they would otherwise be in jail.
Those who trot out the 'but they have DVD players' etc lines are missing the point, I think. It would take a lot more than a DVD player to make me feel anything but wretched in a prison. Sharing a cell with a stranger, not having privacy to shower or use the loo, the constant threat of violence - even relatively small things like having the lights put out at a given time - all of that would be unbearable, and that's without not being with family and friends for so long. I'm sure that it's absolutely horrible, and no amount of TV would make me feel otherwise.
The thing is - none of that is the reason that I don't commit crime - how many people are genuinely deterred by thinking about prison? I, like most people, don't commit crime because I have a legitimate way to make a living, I have been lucky enough to move in non-criminal circles, I was brought up to be be law-abiding, I am neurotypical, I can read, etc etc. I don't need to commit crime, and I don't want to. I don't even consider it, so there is no logical process where I think about it then decide against because of the thought of being locked up.
A lot of people in jail probably wouldn't have done it either if they had been born in a different set of circumstances. I'm not saying that there should be no prisons, but there is no need to make them any worse than they already are.
I don't know how prisoners can best be protected from the virus, though. They are probably safer staying in their cells, but I completely understand the impact that this will have on mental health that is already, for many, compromised.