Why are a high proportion of basic Japanese words written in hiragana?

Question

Sometimes it seems like a lot of basic Japanese words are typically written in hiragana rather than kanji.

By "basic", I mean pleasantries that are probably the first thing non-native speakers learn in Japanese: "おはようございます", "こんにちは", "ください", "ありがとう". Some of these can be written in kanji, for example "ください" can be written as "下さい". One pleasantry that isn't typically written in hiragana is "お願いします".

Are a disproportionate amount of such words typically written in hiragana, and if so, why?

Answer 1

Although it's difficult to show a formal reasoning, it could be said that reducing pointless kanji usage is undeniably an orthographic trend of post-WWII era. "Pointless" roughly means a word no longer preserves the meaning the kanji which assigned to it suggests, or in today's linguistic jargon "semantically bleached".

Things like 補助動詞, including ～てください, are typical examples of semantically bleached words. They're very similar to some English words such as be going to, which now simply indicates time progress without actually going anywhere, and accordingly lost its original spelling becoming gonna. There was a government directive issued in 1981 (and updated in 2010) explicitly named ください and a lot of other words need to be written in kana in official documents.

Greeting clichés are also used without thinking of the original meanings. In English we can say goodbye without fancying how a bad bye would be like (well, etymologically it's from "god be with you"...). Your examples おはようございます, こんにちは, ありがとう seem to be retaining their full form, which in fact not, because:

Expected pronunciations: おはよう{LHHL}ございます{LHHHL}, こんにちは{HLLLL}, ありがとう{LHHHL}

Actual pronunciations: おはようございます{LHHHHHHHL}, こんにちは{LHHHH}, ありがとう{LHLLL}

So it's clear that people no longer take them as a meaningful words they look like. The fact many people spell こんにちわ and こんばんわ instead of は also proves the origin of them has totally forgotten.

Of course these are merely "guideline" and not rigid "rule" so you have no obligation to follow, but it's also true that those conventions are steadily maintained across official, media and pedagogical writings.

Answer 2

A lot of those basic words are related to old expressions. See the kanji that snailboat mentioned in a comment. For example, 御座る (ござる) in おはようおざいます and 有難い (ありがたい) in ありがとう.

It's hard to speak to what is a disproportionate amount. But as to why, consider that basic words like ありがとう and おはよう are learned by Japanese children at a very young age. Children learn hiragana first and when they start learning kanji, they start with simple and basic kanji like 日本 (にほん) rather than those used in 御座る or 有難い.

Of course, these other kanji are learned as Japanese grow older. But you can see why these basic phrases are often written with the more accessible hiragana when you consider that they are some of the earliest words learned by children.