This is from an old codger who has only ridden 56 years, lived in 4 different countries, ridden 1/2 million miles, done drag racing, dirt racing, and Bonneville speed trials. Also have operated a motorcycle repair facility since 1955. During this time, I have met hundreds of riders, bikers, and tramps. I have always made a study of "Why" things work, including people. I feel that the short answer to your question is one word - "PRIDE". Americans, more than any other people I know are inclined to think anything they own is "Best", not based on any hard facts, except that "It's mine, so it is the Best" Note - that this is different from "It is best, thats the reason I own it." I have owned and ridden many different bikes, some bad, some good a couple of great ones. Not to say others would agree with my choice, I do not ask. or expect them to always agree. I have friends and customers who ride most everything imaginable. All are welcome, if you come in with an attitude of "Best because its mine", and get obnoxious about it, you go out. I deal in hard facts, have a load of broken parts in back to show who is strong, who is weak.
All being considered, most modern bikes are as good as the care the owner gives them. I can ride what I please, do not even ride a 'new' bike. I have one I really like, you can have yours. Do not brag about yours, do not bash mine. I will do the same. I am like you and your Panhead. I had one back in 1954, was a worn out piece of junk when I got it. Put a '47 - 74 knuckle engine in it, became a really nice ride. Still nothing I would brag about, but was transportation.
So, give others the respect you want. Their ride means as much to them, as yours does to you. If you do not have a ride - KEEP YOUR MOUTH SHUT!!!! , othen that a compliment.
A friend in Europe said, from his observations, while traveling here, that Americans are the worlds living experts, on what is on the end of their noses, but can not see to their hands. Think about it.
Still here, living it.