Usually having the non-profit status gives you discounts with venue rentals, etc. so that's one reason most comps are non-profit orgs. Also, sponsors are more inclined to donate to a non-profit than a for profit org because that provides the donor with a tax deduction.
Generally speaking, orgs get that non-profit status to save money, rather than donate the profits to charities. The profits made usually go straight to the budget for following year's comp. I could be wrong, and in no way am I speaking on behalf of boston bhangra or any other bhangra comp for that matter.
And no boston bhangra's not the ONLY non-profit comp in the states.