It’s because in Standard Japanese it is something like this:
は[ha̠]
ひ[çi]
ふ[ɸɯ̟ᵝ]
へ[he̞]
ほ[ho̞]
ふ is generally always talked about. But of the remaining, ひ is the only one that is different, and not a voiceless glottal fricative like the rest of them. While /ç/ is also a sound not very present in English, and if you’re a speaker of American English, is pretty much never spoken. If you speak Spanish though it is in “mujer” and for German speakers it is in “nicht”.
@ezekiy し is actually [ɕi] which is obviously very close to [ʃ] and thus generally taught that way. Though for Polish speakers し is the exact same as ś.