I think this is highly dependent upon the person, something I think really isn't being examined enough by those who believe indie games are "easier' to run than traditional... IME they're the people that FATE, PbtA and other indie games just don't click for. I think that for some they just aren't wired to handle constant on the fly improvisation, it never becomes easy for them to create different and dynamic consequences on a fairly regular basis for multiple characters while keeping track of what fiction is generated by said consequences (along with simpler the fiction also generated by simpler action declarations). More importantly they don't have fun running a game in this manner. As an example I don't think a DM with anxiety issues would feel comfortable enough to run in this manner very well (mush less consider it something fun to do). I think for many, though it may be more intensive prep wise (and much less so while running the game), it is easier to have something they can fall back on as a foundation...whether that is an entire adventure path or simply the bullet point notes that @hawkeyefan spoke to earlier.
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Oh wow, that reminds me of some GMs that thought they were really so good at the improv juggling until I sat down and pointed out the absolutely massive plot holes, refrigerator moments, and inconsistencies that had crept in like 4 sessions!
I tend to keep very close track on things as I am constantly looking for patterns in hopes of finding something to exploit. I had to stop because absolutely nothing was lining up. I began to feel like I was either in a demented nightmare or was a paranoid schizophrenic seeing connections where none existed. Letting go and treating each scene as independent made things easier, but was very unrewarding.