https://www.film-shorts.tv/wpress.cfonseca160/blog/2020/09/13/newsweek-article-explains/

This ‘Newsweek’ article gives a brief depiction as to why the current policy of 34 states is quite prudent, if you see it as I do. They say, “they [those states] will not accept ballots that arrive after election day Nov. 3, 2020.” [as other states will.]
(Not all states have the same deadlines for submitting ballot: problem, as I see it).