There are Japanese words that are written in Kana frequently despite having an associated Kanji (i.e. 轢かれる > ひかれる) like how 鰻 is often written as うなぎ when used as signage, is it because the Kanji is too difficult? They also do this in words where partial Kana is used rather than the actual Kanji altogether (i.e. 信憑性 > 信ぴょう性). I’ve also seen this in words such as: 刎頸 (ふんけい), 膀胱癌 (ぼうこうがん), 躊躇 (ちゅうちょ), 兎 (うさぎ), 髑髏 (どくろ), 鰐, (わに), 蝿 (はえ), 癇癪 (かんしゃく), 胆のう (嚢 exists, just use it) and so on…
i also find the inconsistency irritating.
in addition to the 常用 distinction, signage , for example, has a different set of requirements compared to books, etc, and different audience capabilities. most people know how to read 鰻 but from far away along a sidewalk, it may be too blurry to attract customers. in that context, there is competition between easier to read signs.
also, you may notice some terms for things like reading glasses, various diseases and other elderly-targeted items would also be in kana sometimes. kanji objectively has more detail than kana or romaji at the same don’t sizes, so vision capability is a factor. also visual euphemism effect is a factor as far as embarrassment, ヂ vs 痔.
also it’s standard to write many of the animal and plant species names in katakana. this is partly for standardization in the sense that some of the names come from foreign languages. and even in English, species names are often italicized. furthermore, many of the kanji names of species are 当て字 so their legitimacy vis-à-vis matching the pronunciation is debatable.
there are many inconsistencies more aggravating than this in Japanese. not to tell you to get over it, i also haven’t.
indeed some of these examples are reasons for some of the unexpected used of kana, as well as other differentiation techniques like use of お/ご prefixes when not required by grammar/etiquette rules.