I think this comes down to dealers, bike and parts manufacturers marketing. There is a difference between "custom" and "customized" and the dealers especially conflate those terms all the time. Over time the terms have lost meaning for both "custom" and "bobber".
Bolting on a different do-dad than what came stock does not make it a custom bike. It is customized. It is not upgraded, there is just cosmetic changes that the next owner may or may not care about. I love the ads that list "over $5k in upgrades!". Nah, those aren't upgrades, buddy, you took a stock bike and made it ugly with a bunch of crap from China sold by brands with cool names.
But the manufacturers hold guilt with this too. Indian took a Scout, swapped out the fenders and called it a Bobber. It's not a bobber in the traditional sense, since the changes are cosmetic and didn't result in any real weight loss. The original bobbers were really cut down bikes, lot of them even ditching the front brake for weight savings. But the idea of a bobber is cool so now two companies have models they call Bobber, that are just solo seat version of an existing model.
This isn't new or unique to "custom bobber" as a term. Look at how many people misuse the term "suicide shift" or "suicide clutch" when they slap a hand shifter on a bike. To be a suicide shift the bike has to have a foot clutch, a hand shift and no front brake. The whole reason it got the name "suicide" is because you can only have one foot down at a time, so you have to release the rear brake, your only brake, to operate the clutch to get going. But over the years the concept got watered down and now lots of guys install a hand shifter and misuse the term. It's all just marketing and posturing. It exists in all modern industries.
