It absolutely is a reason. Everyone else is doing it, meaning if you don't you feel isolated.
So, either you participate and feel isolated through your social connections by social media, or you don't participate and feel even more isolated because you don't have social connections.
Again you miss the point entirely. This is not Apple vs Android. This is teenagers not being given a choice whether or not to use social media generally.
The fact is if everyone else uses it, this precludes them from many normal interactions that get replaced by social media. It's a cultural thing as much as it is a personal thing. You will feel excluded if you don't use it, so unless everyone changes, it's hard for you to change. That takes a determination even many adults lack.
The harmful effects of social media are not eliminated by choosing not to participate. They have a cultural impact (both benefit and harm) that expands beyond an individuals choice. We should reconsider how to handle teenagers on social media as a society. Not just tell them to preclude themselves if it's harming them.
So, either you participate and feel isolated through your social connections by social media, or you don't participate and feel even more isolated because you don't have social connections.