It's steroids and hard work. Most people can achieve a comparable look (of marvel movies, not mass monster bodybuilders) with years of hard work, with the exception of maybe some delt size.
And thus the missing component ultimately is roids really.
Because if you don't use roids, by far most people can't get roided tiktoker/marvel super hero look. Hard work or not.
The fact is, that most actors in those movies get there very quickly, relatively speaking and they do use roids. With some very, very rare exceptions.
The hard work isn't the missing component, the roids is the missing key component.