That's not entirely true. President Elect Trump himself spent the greater part of a month prior to the election claiming repeatedly that the election was "absolutely" rigged and, if you remember, predicated his unconditional acceptance of the results on his victory. People of a conspiratorial bent were already primed by his muddying of the waters so it shouldn't be a surprise that his own upset victory would be met with challenge.

Not to mention that this entire election cycle was one where bad actors from all directions took advantage of the poor discernment of the American electorate to the point where truth, innuendo, dubious claims and outright lies were given equal weight in the decision making process of many. Informational chaos has now been proven to be a winning strategy (and not just because Trump won) so why wouldn't that carry on post-election?