Because it decreases self-confidence and initiative. It makes you think of the things that the "hero" does as exceptional and out of your reach, instead of something you could do as well if you put your mind to it properly.
'Hero Worship' is about elevating someone to a categorically higher level. This can lead to thinking you could never be as good, taking everything they say as gospel, defending even their poor opinions, etc.
If we -worship- 10x developers, you can maybe better see how with the emphasis on that word things can get pretty toxic pretty quick. For example, I think many would agree HR disputes should not take talent level as an input, but if one of those people isn't even a mortal...
---
None of this is necessary to have a role model, or precludes celebrating someone for doing excellent work as is this case.