1. Because fiction, anyway fiction doesn't treat black hole as serious as real life, and in real life you can't get past SoL speed.
2. Now come to real life, the reason why you can escapes a black hole with FTL speed is because in theory that speed make you run backward in time, and that could mean FTL in real life is Immeasurable speed if we use our wiki standard. But in fiction you can go MFTL+ like crazy but you doesn't run backward in time by anymean, thus default speed for outrun a Black Hole absorption is FTL. Unless the verse specific on this thing with extreme evidence and context.
DCEU Flash run backward in time by moving at FTL speed, but what he get on our wiki is FTL speed with Time Travel hax, if we give him Immeasurable speed we must also give that speed to everyone else with FTL and beyond. So....
3. Also Immeasurable speed mean you speed is beyond temporal axis, thus you can freely move and attack at any moment in time, or specifically any point on the time axis, simply outrun a Black Hole doesn't mean this even though Black Hole bend and drag space-time