I don't see the big deal unless someone tries to make it something its not. They're monsters, nothing more. See the boy's version named Cool Ghoul? Both bikes have monsters pictured. That's all they are. Sheesh!
Since the door is open here's a take on it:
These bikes were made at a time when the word was used by some Americans to demean other Americans, much more broadly and openly than it is today.
The meaning and intent was and is still widely known.
Many Americans didn't have the privilege of seeing that bike as innocuous.
Given that, it's both surprising, and unfortunately not, that it made it onto that chain guard.
The 1970s were not far removed from accepted and legal discrimination in this country.
Perhaps one can empathize with the reactions people had, and perhaps still have, to seeing that bike.
Some dealt with discrimination and bigotry, coarse and subtle, pretty much all day every day; some dealt it out.
IMO understanding this and then choosing to dismiss or minimize the implication is callous.