A firework rocket is stabilised by the weight of the stick, same principle as a wire-walker - get the c of g low enough and it can't fall over but at a huge cost to it's load carrying performance.
To prove this take a firework rocket and support it with a finger at the bottom of the tube where the fuse is ie the point where thrust is applied. It will sit upright on your fingertip quite happily. Remove the stick and try again - different result.
Hanging 1000ft of 30 inch gas pipeline behind a Saturn 5 was never going to catch on so they had to think of something else!