Why do so many movies with quiet, somber endings immediately cut to loud, bombastic music when the credits start?

Basically the title. I was watching Blade Runner 2049 when I was reminded of this weird trend, although I've definitely seen it happen plenty of other times (BvS is another one off the top of my head). What's the deal with movies ending on a quiet, often sad note with fitting music to accompany the scene suddenly turning up to the climax again when the credits start? The transition is so jarring, why not continue with similar music to let the ending breath? What's the reasoning behind this? Does the director decide this or is there some weird rule that the main theme or whatever has to go at the start of the credits? I tried searching around for similar threads but couldn't find any. This is something I've noticed for a while but never understood the reasoning behind. Anybody know why this happens?

Submitted October 09, 2017 at 08:02PM by Lovlace_Valentino http://ift.tt/2gpGMTy