If hdrmerge gets the “best” pixels from three original images, then it results in a 32-bit composite with the best from each image, without demosaicing.
Then you must recover all that good information, aka high dynamic range, and make it visible in a low dynamic range image.
The 5 exposures generations is just a way of cheating enfuse to give it all the high dynamic range possible for its compression.
Why 5 and not 3? Well…to give enfuse more dynamic range layers?
I feel I’m only scratching the surface, and it would be nice to hear a more scientific answer from @Carmelo_DrRaw , but this superficial rationale (due to my lack of deep understanding of what’s involved here) is what drives my attempt to use this workflow (besides the fact that it gave excellent results in that original post)
Anyway, be aware that he brought an alternative way of compressing the hdr based on the bilateral filter.
EDIT: As for the noise, I think it’s similar to what you get when you stack layers using mean or median, Try to stack those five layers in Gimp, for example, and you’ll get a less noisy image.
EDIT2: Actually, I think the best stacking mode to reduce noise is median. Maybe the mean, or average, method works well if you dither your layers by some pixels (and also here), The last links I provided are for astrophotography but I suspect it could give good results for any kind of image (provided you’re up to spend thousands of $ to buy a telescope mount capable of dithering 
).