Maybe it's because most pipes now have high coverage heat shields to hide the head pipes? I've never had a blueing problem with mufflers.
I have a Shovelhead and put chrome shotgun duals on it a few years ago. Pipes blued about 10" back from the heads on the first ride around the block. An' that Shovel ain't running nowhere near lean.
By some error either mine or the shop that worked on my bike last, I blued the crap out of one of my slip ons. I was pissed but corrected it. My local plater is charging me $50 to
re chrome the muffler. I think that is why people are not so worried about it. That is the cheapest fix I have had for a screw up in a long time.
In the old days (late 60's) there was only a little blueing and yellowing near the attachment at the head.
Now they are so lean and turning blue, the MoCo put the heat resistant shields over the pipes down to the mufflers that don't turn blue. I cant see the bluing unless looking just right at the reflection on the oil tank. Truly OUT OF SIGHT OUT OF MIND.
Semichrome worked great back then, but wont do a thing for the bluing now. It's an excellent chrome polish for all the non blued chrome.
If I start to worry about bluing then I would worry about getting dirt and road grime
I just over look it and ride as many miles as I can wash the bike once a week if I can
not show room bike but id ride her any ware