Why are mice such good candidates for scientific research on various things in psychology and neuroscience? Why not, say, squirrels (or some other arbitrarily chosen small mammal) instead?
I'll go out on a limb and say I think it's because mice breed more easily/faster or have more young so there's a good stock of replacement mice.
Squirrels also have a lot of fur (e.g. on their tail) so the risk of a researcher being allergic to them is probably higher.