Some of the people will not go out of their rooms because they are afraid they will soil themselves, and they lose out on the social interaction.
Some of them are too weak and/or too overweight to stand up to go to the toilet and end up falling.
Some of them are too forgetful and get stool smeared all over themselves with their hands and everyone else. This is an unsafe risk for infection for everyone else.
By the time a person lives in a nursing home, they usually have very little choice left because of the decrease in many of their body's functions, including bowel function. In reality, you are not shocked by the large and varied selection of adult briefs at the local store, but are being forced by unfortunate circumstances to look at the changes effecting your dad's life.
Every week at work I get someone in that has lived by themselves or with a spouse that needs to look at moving to a nursing home. They become ill and we get them over the illness, sometimes, but it shines a bright light on changes that they have struggled very hard to hide. The confusion, the bruises, the falls, the lack of understanding of their medications, malnutrition, loss of financial control, memory loss, burns, sores, tumors, loss of hearing, loss of vision all become apparent and painful for the families to see.