Kinda makes me wonder what would have happened if the Japanese continued to make I-4 cruisers like the Eliminator 900/1000, Maxim X or V-4s like the V-Max, Suzuki Madura, Honda Magna line instead of opting to build It's much bikes with V-Twin motors that are "less efficient than an engine of a different configuration but identical displacement" that "vibrates more, and it's less reliable than other more modern configurations" for the sake of character or style.
Well it's what the market wants. It's not like V-Twins are without advantages. Style is one, low end torque is another, and certainly the sound and personality are there. Easy to work on, fewer parts, etc.
It's not like the other bikes are gone. Remember those old inline bikes had a 'standard' riding position (upright, feet directly below you, etc.) Today we call that a 'sport tourer' and they truly are the next generation of those Kawasaki KZ's, Suzuki GS's, etc. Bikes like the Honda ST1300, Kawasaki ZX-14, etc. are really the top notch option. Some might go so far as to say that a sport touring bike is a 'correct' motorcycle. It has the most efficient engines, the riding position that allows the most control of the bike and the best lean angles, and features that V-Twin cruisers will probably never have (like electrically adjustable windshields, etc.) But, many of us, myself included, are still drawn to V-Twin cruisers for a variety of options! The Inline and Boxer type engines are too wide to allow for forward mounted controls, for one example.
A cruiser with a super smooth and powerful inline twin (2 cylinder) does exist, it's made by triumph and comes in a few models! They are out there, it's just the biggest chunk of the market is the V-Twin Cruiser. It's what people want! Few riders ride more than a few thousand miles on their bikes each year, so they are more than willing to sacrifice 'practical' comfortable bikes and replace them with bikes that are a little 'cooler'. Then there are oddballs like me and many many others who DO ride quite a bit but still enjoy the throaty rumble and laid back ride of a V-Twin cruiser, so much so that we'd prefer it over a smoother more powerful bike.
I know people call some of those old bikes Cruisers but I really don't think they are. The MSF book calls them 'standards'. To me, a cruiser has wider, taller handlebars, and most importantly, feet forward riding positions. Those bikes you mentioned all had the pegs mounted directly below the seat. Due to the wider engines, only highway pegs could be mounted up farther.