For one thing the bright sparkling scenes do have to be linked together somehow. And what looks good in isolation does not always work when you are trying to fit all the gems elegantly together into a piece of jewelry. Sometimes they have to be an odd shape to fit in their place. And all the time you have to neatly solder them in place and get the gold or silver buffed to brilliance about them.
Or, to vary the metaphor, since the story flows like a river, ideally bearing the reader down it swiftly and with snags, it can be awkward to try to link existing bodies of water together. Better to go with the flow and so link them.
And if the sparkling scenes are more interesting, it means that the dull work of transitioning is more evenly spread out.
At least for me. I have heard that other writers manage to work out of order.