Kollelim help baalei batim to learn and provide affordable teachers to local schools. Thus, these baalei batim stay in the town and feel more attached to learning, and also give to Chabad houses who connect to non-observant. Thus, Kollelim indirectly contribute to the Chabad activities.
R Salanter saw such connections in spiritual world: when something is not learning well in vilno, a professor in Paris becomes an apikoires or something like that.