FH is heavily derived from the human-rated F9, but what capsule would fly on FH? Crew Dragon flies fine on F9, and NASA isn't looking to fly Orion on FH. If the latter part changed I'm sure SpaceX would undertake the human rating.

This has actually caused some interesting dynamics:

- To get F9 human-rated, SpaceX had to perform many successful launches using the same configuration.

- Keeping the same configuration essentially froze any further development of F9.

- Development focus switched to a green-field successor, the BFR/Starship.

- Announcement of BFR/Starship caused an Osborne Effect for Falcon Heavy: anyone considering it (even SpaceX themselves!) would be better off waiting to see if Starship works https://en.wikipedia.org/wiki/Osborne_effect

- This stifled Falcon Heavy's market (which was already questionable/nascent), resulting in very few launches

- Having very few launches makes it hard to human-rate Falcon Heavy (in any case, SpaceX have bet the house on Starship)

Why to have a larger than necessary rocket, which has additional problems with just getting stuff to orbit - FH is more complex than F9 - to carry humans, who requires extra care?

Much better, from the point of safety, is to have a moderate-sized launcher human rated and specializing in bringing humans safely to orbit. After that it's much safer to use whatever means of travel are brought to space by any other launchers, those with focus on economy and less on safety.

A counterargument is usually a variation of "it's very expensive", but that's just, roughly, because human life is valued cheap enough to allow for suboptimal choices.

https://caseyhandmer.wordpress.com/2021/02/24/sls-is-cancell...