Why the bare metal patches

[Humptyfish]

Sorry if this is a stupid question, but
Why are there a pair of patches of frame either side which are left unpainted. I asked my dealer when I first looked in the show room thinking something was missing (they didnt know)
I get that the engine bolts go through them and the crash bungs fit there. I also expect that as they are polished/ground flat that the bike/engine is probably hung from there during the build but I dont get why they are left like that. It just looks odd (like something fell off)

 

[bricrewe]

It does look a bit shite doesn't it. I've wondered why its like that aswel

 

[r25sti]

im guessing to give a nice flat surface for the nut/bolt and to match machining on swingarm. i do agree, there not nice.