The advantage I saw of asking questions is to make sure what you've explained is understood. Sometimes you'll ask me for example what the に does in a certain sentence, it's a great way to check acquisitions I think!
So instead of just saying thank you for the replies I'll reformulate from now on starting now:
"Think about the difference between 日本のことを知る and 雪があまり降らない. The former is the subject's volitional action. The subject of the main clause 私 can control whether they (try to) know about Japan or not."
In the first sentence 私は日本のことを知るため(に)日本へ行く the subject wants to do something. In the first clause (preceding ため the speaker has a choice to want to know Japan more or not.
On the other hand, 雪が降る/降らない is a non-volitional action, and the subject can't (or no one can) control it.
In that sentence, the speaker has no control or choice whether snow will fall or not.
Actually, this is the key of the two different meanings of ため. ため means "in order to" for the former case, and it's "because" in the latter.
ため has two main meanings, "in order to" and "because". Whether or not volition plays a role will determine which one if the two meanings it is.
As for 物を売る仕事になかなか人が集まらない, 集まる can be a volitional verb, but the subject of the main clause (shops/shop owners) can't control whether or not people are attracted to the job. That's why ため means "because" in the news article.
Even though 集まる can be volitional, it's not the case here because the owners can't influence the attraction to the job so it's because. When there is volition, it's "in order to" when there is volition "it's because".
私は日本のことを知らないため、日本へ行きます。
Volition: in order to
今年は雪がたくさん降るため、スキーができます。
No volition: because
店で働く人を集めるため、休みを多くしました。
Volition: in order to, the workers they have control to gather or not. In order to.
ライバル店が人をたくさん集めるため、経営が厳しくなっています。
This one is more difficult as I don't know what a Rival store is but I think it's because. I think the management is reacting to something they have no control on in the first clause. Because.