They are saved for sporting events.
Their use on railways, that’s one I had heard of. Although I think I’m right in saying that audible explosive charges are/were the prefered ‘last ditch’ warning signal - three placed on the rail, on after another, so they go off in sequence as the train rolls over them. The obvious advanrage of these is there’s no potential to cause distractions or visibility problems to anything or anyone else.
The other point about maritime flares is that they’re intended to be held and waved. Although not to be thrown.
…errr, I meant the preferred warning signal in Britain.
The flares which are approved by the US Coast Guard for waving on boats are intended to be held in one’s hand. Here, a boating safety instructor shows
how to hold the flare so that it doesn’t drip burning stuff on the deck (or one’s feet.)
I can’t imagine using them at a US football game, but I am from the home of the Oakland Raiders, so practically anything could happen. 
The boat flares look a lot like the ones sold at auto supply stores for motorists to put on the road in case of a breakdown, but the latter won’t have the USCG approval and expiration date that water cops expect to see during an inspection of vessel safety equipment.