So old Japanese motorbikes don't have liners stock? Other than being a quick way to fix pinholes, I see it like putting super glue and rubber on a tire.
Not that I have come across but I haven't seen every tank from every manufacturer on the inside.
I can tell you from personal experience, that in order to fix badly damaged tanks, it is sometimes absolutely necessary to re-line them. Or, you must cut the tank shell free from the tunnel, work a patch to the curves, weld it in, grind it, hammer and dolly the metal, then, weld the tank back together. Would cost you right around $1,000 to do it that way.
Or, with some decent patch work, some tig welding and grinding, a liner insures that the patch is leakproof. So, sometimes, it's a matter of economics for folks on a budget who desire to retain the original tank.
And I don't know how much bodywork you've done, but Bondo is absolutely used on
every show car to attain perfect lines. Bondo isn't the foe, gobbling it into dents to raise the surface by amateurs is. But every pro "surfaces" body panels to produce perfectly straight and flawless paint jobs. And they're not cheap either...