Given Marvel and similar franchises at the cinema around the same period, it was a breath of fresh air (also a great film)
The X-Men films have the property you want, with plots and characterization included in the movie instead of relying on you to bring them with you in your mind.
(Are the later films good? They're not great, but if you watch one you'll come out with a sense that the movie had a plot, the things that happened were related to that plot, and the characters had reasons for the things they were doing. The films are quite inconsistent with each other, but they're very coherent considered individually.)
The MCU films of phase 2 have already lost it. (For context, phase 2 starts with Iron Man 3 and is mostly garbage with the exception of Winter Soldier, concluding with Ant-Man.)
My conclusion is basically just that someone at the MCU decided "we can save on the budget if we stop using writers".
This is something that everyone wants.
> If you need a good plot it adds a lot of uncertainty into which script, how long it will take to write, etc.
This is true of everything too.
Why would these common factors only lead the MCU to abandon the idea of plotting its movies? How come Moana had a plot?