Because people do care and he knows that.
I'm just pointing out that saying "zoo, if you're reading this, I hope you're doing okay and you'll be back soon" might be a bit more empathetic than
"day 18 of the zoo watch
let's see who can come up with the best reason for him being awol."
But I think that's how you show your concern and he probably knows you well enough to know that.
thank you for letting me know how to show someone that you care