Why is 大家们 (dàjiāmén) a thing? Searching Baidu for 大家们 (dàjiāmén) gives 8,770,000 hits.

Question: Why is 大家们 a thing?

It is surprising because 大家 (dàjiā) means everyone, and 们 (mén) is used to turn a few select words into plurals.  For example, 我们 (wǒmén = us, we), 先生们 (xiānshēngmén = gentlemen), and 朋友们 (péngyǒumén = friends).

It doesn't seem to make sense to say 大家们 and take a plural of "everyone".
大家们 is not correct.

Not all search terms with a lot of results are correct words/phrases.

You should notice that there are not many meaningful results in the search results. And the very first result is a Q/A site asking whether "大家们" is correct, and the accept answer says it is not. The second result is a paper from a journal that discusses this kind of errors.