Use of わたし vs 私

[BigEm]

So I’m doing some studying with the Kanzen Master N3 books, and they always use the hiragana わたし instead of the kanji 私. Is this some sort of more standard usage, like 子ども instead of 子供, or is the book simply assuming I don’t know the kanji? It’s kinda annoying me tbh

Here are a few of the example sentences where this has occurred:

わたしなんかまだまだ勉強が足りません。

この車はわたしにも買えるくらいの値段だ。

わたしは今年７７歳ですが、まだまだ若いつもりです。

Thanks in advance!

[Leebo]

Since 私 can be read わたし or わたくし, careful writers might avoid the kanji to be extra sure you can read it correctly.

It’s kind of like how on TV news or weather you’ll often see きょう or あす, even though everyone can read the kanji forms. They just want to avoid making people think about which reading it could be.

[BigEm]

Ah, that makes sense. Thanks so much!