Because there have not been any serious reports of fraud and abuse, and the things he built are so important for the future of humanity, that even much more serious accusations won't change the total balance to a negative for Musk.
There have been dozens of articles detailing fraud and abuse at Tesla, quite a few articles about Boring Co's liberties with the truth and its outright lies to the people in the neighborhood where the tunnel is being built. SolarCity's financials were so bad they went through multiple auditing firms before they found one that would sign off on them.
All in all, Musk's companies have an above-average incidence of ethics- and truth-related issues.
I recently traveled to Florida and met with my cousin that has friends at SpaceX. The joke is to call it SlaveX. According to him, it pays quite a bit better than ULA, but there’s huge burnout and turnover.
> Why is there a cult following when fraud and employee abuse is common?
Musk can present an image of a successful multiple entrepreneur who is working towards a vision that many support arrayed against a forces of Big Bad Incumbents who would rather squash him than compete fairly. Thus he is responsible for all the good things, and the bad things are just smear campaigns that should be ignored.
Essentially, it's the same force that fuels the rise of people like Trump, just applied to a different part of the political spectrum.
It's because Musk has cultivated a tech-god image for the last decade.
From cameos in movies and tv shows to projects like SpaceX that were created solely to boost his "genius" image, Musk (or his publicists) have done everything to make him seem like a superhuman.