That's because it simply isn't, and, frankly, it's extremely insulting to suggest that the shortening of Japanese to Jap, like you would Briton to Brit, is even on par with calling someone the N-word.
Best let the Japanese decide how offended they are by the use of the word 'Jap'. And let's not get into a contest about what's more offensive.
How exactly would you determine whether something was 'hate speech' (whatever that means...) and had 'racially offensive overtones'? Is it purely based on the person's opinion? If so then that's a funny rule to have that is based on no hard or fast definition.
If the language offends that person, then it's 'hate speech'. At the very least, respect that person's opinion and don't use it.
Surprising considering the average Japanese person isn't an English speaker.
Actually, the Japanese are taught English as a second language at school. Granted, individuals will have differing abilities, but in my experience most understand English reasonably well.