The mouse utopia experiment is nothing like having a pet mouse. Its more like exploring the way mice react to being institutuionalized. Its been a while since i read about it so i dont recall how much excersize or enrichment the mice had access to.

But from what i recall id call it more like a prison where all their needs are met and they have absolutely zero responsibilities, thus their current choices have zero impact on their future quality of life.

In people id expect that to lead to depression and mental illness which is basically what we saw in the mice. Im not convinced this experiment could be considered a utopia any more than a coed prison which also provides, food water and shelter but not entertainment or enrichment/stimulus.

Without entertainment/enrichment/stimulus even humans develop all sorts of problems like dementia, just look at nursing homes/classical assylums for the human equivalent/example.

The nuance is it wasn't a utopia because eventually the population of mice were extremely overcrowded: that's when things circled the drain. If you trapped a bunch of humans where they had no personal space ever they would all also go insane.