Saying that if a movie opens below $357M it's because of lack of interest is one of the most ludicrous things i've ever heard. Endgame was basically the most anticipated (and hyped) a collective public has been for a film in the history of movie going.
$357M opening will likely not be broken for at least 5-10 years, if ever. And to get that opening, as
@TheGentTrent pointed out, theaters had to stay open 24/7.