Focused when I pray alone, scattered behind the imam

I can pray in my tiny Freetown room and everything lines up. At fajr I kneel on the thin mat, the street still, the kettle forgotten on the stove, and the words sit in my chest like something true. But when I walk to the mosque and stand in a row behind the imam, my mind scatters: the bus driver who owes me money, a message left on read, a child I need to call. My eyes follow the imam but my heart is somewhere else. Why does congregation pull my attention away when private prayer can feel so full? Has anyone else lived this, and what did you notice?