We used to track inactivity as the leisure time of workers or devices. But why not use inactivity monitoring in terms of personal safety? A modern person, regardless of age, starts the day with the smartphone and goes to bed with it (OK, that's not a healthy habit, but raise your hand if you don't)
If we set an inactivity time and an app sends us an alert when the phone isn't used for longer, that will be a timely sign of your loved one requiring help. So I think, when choosing a personal safety app for one we really care about, inactivity monitoring is a necessary feature.