For me, dynasty takes significantly more time/effort/thought than redraft.
Dynasty is year-round, redraft only lasts a little longer than the NFL season. In-season management is not that different between the formats, but dynasty involves way more off-season work.
In dynasty, most roster changes require trades (which tend to involve a fair amount of thinking, discussions, and efforts which wind up not amounting to anything). In redraft, most of it comes in the draft which takes only a couple hours in its entirety. If you thought a year ago that Doug Martin was underrated, and now you think he's overrated, in dynasty acting on that would mean trying to trade for him last offseason and trying to trade him away now. In redraft, you could just choose to draft him last year and to not draft him this year.
More players are fantasy-relevant in dynasty. You have to think about what you eventually expect to see from Nelson Agholor, Jerick McKinnon, Jared Goff, Maxx Williams, etc., and make moves to fill your roster with prospects that you like. In redraft, you're mostly focused on current fantasy starters plus a few backups or guys with upside.
I find dynasty more fun than redraft, although I also enjoy draft-only best ball redraft leagues a lot (which go even farther in the direction of less time/effort).