Marvel is known for its event cycle. The publisher used to just one big summer crossover event, but as the success of these comics became more apparent, Marvel went all in on making event books. Most of the time, these event books get comics that build into them, but other times they come out of nowhere. However, even the ones that have a build build-up usually use plenty of room for prequels.
Source：https://www.cbr.com/marvel-events-should-have-prequels/
