On the intellectual level I have absolutely no reason to doubt the scientific evidence or the countless accounts of people who were subjected to solitary imprisonment and describe it as torture and worst thing that ever happened to them. I remember a documentary (probably NatGeo's "America's hardest prisons") episode where a violent and seemingly fearless thug was reduced to a crying baby by 2 weeks of solitary confi…
It's simple, if you want to. You just haven't had a comparable experience.
Lock yourself in a room with no contact with the outside world for a month or two. Remove any niceties a prison would not allow. Probably a room with no windows, mirror, or books.
If you aren't willing to do it, explore what you lose in life. Try doing it for a day or even an hour.
Maybe the difficulty in empathizing comes from the difference from anything you consider a normal life.