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For more than 100 years, very large events have made the key participants, of the event, notable beyond that single event. Also, several phrases or small places have also become notable from a single event, and therefore, Wikipedia has separate articles for those topics. The general rule, in many cases, is to cover the event, not the person. However, as both the event and the individual's role grow larger, separate articles become justified.
The Wikipedia guidelines WP:Notability (people) & WP:BLP note that most small-scale events do not generate notability for the participants at those events. However, the result is different for big, highly-significant events that affect large numbers of people. The first example, given in WP:BLP (in July 2009), is for notable person John Hinckley, Jr., who had tried to assassinate U.S. President Ronald Reagan in 1981. As an independent article, detailed facts about Hinckley can be kept separate from articles about President Reagan or others involved, rather than being repeated within each.
The following big events have made several key people/phrases notable:
The sinking of the R.M.S. Titanic generated several notables in 1912:
Manson family, followers of Manson (some at the scene)
Helter Skelter, struggle Manson said would end the world.
In general, most events are not of a large enough scale to make the key participants notable. However, others generate such mainstream coverage that the key people, or companies, or products, or places, or other names become separately notable, as almost household names for the general public.
In summary, as noted in Wikipedia guideline WP:Notability (people), some highly publicized events have made the key participants instantly notable, due to having a major role or impact in the event. Hence, separate articles have become justified.