A lot of it has to do with resale value. Vincents have a pretty high resale, so any little bit of remaining Vincent DNA gets turned into a functioning machine. This is relatively easy(but expensive) to do since the Vincent spares company can sell you every part needed to make a complete bike. No doubt there have been multiple bikes built from the remains of a single bike in some cases.
I dont know the exact percentage of postwar bikes that still exist, but it is extremely high. When it comes to the really rare models, there has been some skulduggery. It has been said of the famous Black Lightning model that 38 of the original 30 built are still in existence!
Hondas would generally be at the other end of the spectrum in terms of survivng percentages. For many years they were of little or no value once worn out and needing a rebuild, so off to the dump they went.
Im familiar with the Hondas from the sixties, the little guys. The biggest machine made by them in those days was the 450. Most of the bikes I repaired or rebuilt were the 50cc thru to 350 cc size. They were reliable little sloggers, as noted above, not overly inspiring in the performance department, and actually quite short lived. The metal was so soft that motors seldom got more than 10 k before needing a ring job, then a light hone and another 5k to throw away time. I understand that all of that changed in the 70s
In the looks department, I have a hard time coming up with any Japanese or American built bike from the fifties or sixties that comes close to the Brits. Put the poor old Honda 305 or 250 Dream alongside a BSA Goldstar and Im afraid the Goldie would get the lions share of attention. Tho the Brits had some ugly bikes too, it seems they had a lot that were very desirable then and now.
In addition to the Goldstar dbd34, which I think is simply the most beautiful bike ever built, close behind there is the Norton Dominator, the Commando, the Triumph 650 and 500 models, the Royal Enfield Interceptor, any preunit BSA twin, the Velos and a few others im not thinking of right now. The Brits all seem to have the right look along with performance to match.
I guess Im not alone in that thinking, judging by the price escalation that has gone on with many of the sportier British Bikes.
Glen