Because you raise the question of why does the world seem surprised at Iron Man when they've already seen the Fantastic Four? Ant-Man worked in secret in the MCU, so the public didn't know he existed.
My main reason is that the F4 if you go by
their
powers and code names they don't fit a current context.
This makes no sense.
What we see and what we seem are but a dream. A dream within a dream.

My main reason is that the F4 if you go by there powers and code names they don't fit a current context.
Like Ant-Man if you open up the idea of the character having existed earlier decades when a code name like that would be easier to get away with it allows for the jokes and one-liners to come out.
The F4 were the original heroes of Marvel the first family why not go with the idea of them having been earlier heroes before Tony brought on the modern superhero.

IF and When Marvel gets the rights back,can't they just Insert the FF into the current timeline? Do they really need to of existed decades before? I have heard similar ideas and honestly I think it would be more simple to have them exist in the current timeline and have them go to space
Ask the guards, they'll deny it. Ask the inmates herethey'll cut their tongues out before they talk

Somebody could always create another android, call it the Human Torch.

No. This idea is unnecessarily complicated when the original origin could easily be updated with information and ideas about current space research and exploration.
What we see and what we seem are but a dream. A dream within a dream.