To be fair, sometimes, they don’t.
I just got 頼み as a noun, and the example sentence was
in which they just use the past tense of 頼む, the verb.
But even besides situations like that, often the example sentences do use an alternative meaning of the word that isn’t listed as one of possible definitions by the site, or as part of colloquial phrases, or as like half to a third of a 熟語.
I mean, granted, it is using the kanji, but if you’re being drilled on a discrete vocabulary item, the example sentence should theoretically use that vocabulary item and not just the kanji in it.
As a corollary, it’d be like if you were learning English and I gave you the vocab word “viscera” and the example sentence “Jon Stewart straight up eviscerated President Bush on last night’s Daily Show, ammirite?” I mean the two terms are definitely related, but it’d be super confusing to an EFL student and would be potentially misleading about the context for the usage of the word you’re supposed to be being taught.
EDIT: Apropros, the vocab I literally just learned was
遺伝子 (genes), but the sentence was
in which 遺伝子検査 does not mean “karyotype” but “paternity test,” and that still leaves me without an example of the word 遺伝子 being used in a sentence so I don’t know if its colloquial like “genes” is in English, or technical, like “genomes” is. Granted, I can probably infer that based off the english translation, but I couldn’t do that for example with WK’s 4 different versions of “consent” or 3 different versions of “reality” or “truth”