If you don't live in a society but in some remote wilderness and hunt for your food, then you don't need to care what others do.
If you do live in a society, you do need to care, as "what others do" affects society in general, including you in the end. Affects how they behave, how they vote, what causes they support, their mental health, and tons of other things, all of which end up also affecting those who don't use those apps.
If you do live in a society, you do need to care, as "what others do" affects society in general, including you in the end. Affects how they behave, how they vote, what causes they support, their mental health, and tons of other things, all of which end up also affecting those who don't use those apps.