If the frizzen is too soft, it won't spark. The flint will actually bite into the metal and stop partway down the face of the frizzen. Also the flint may fracture bady, because it has bitten into the metal of the frizzen instead of scraping over it.
Your frizzen does not look that soft. There would be a big groove across the top where the flint hits.
Tell me, what color are the sparks? A dull red spark may mean that the frizzen is barely hard enough. A yellow/white spark means it's as hard as you want it to be.
You can try other kinds of flint, such as French blondes, or Missouri white. Try bevel up and bevel down, and vary the distance extending from the top jaw. If you find some combination that works, for Job's sake, write it down.