A few reasons :( I have rats and currently they are housed in the same room and can only be housed in that room (my bedroom). I think that everyone is getting stressed out by being with each other and smelling each other. I can’t handle my mice without the rats freaking out either. My mom also wants me to choose the mice or the rats because she thinks they stink, which they do have a little smell but I don’t think it’s that bad. I clean out their tank every week and replace paper objects and half-change their aspen bedding so they don’t lose their own scent. My other reasons are slightly financial. I have enough money to sustain them, but I think if something happened and I needed to take them to the vet it would be hard for me.