As far as how modern "classics" look, there are MANY considerations that were not factors back in the 50s-70s.
Besides all the government restrictions on sound/noise, carbon emissions, etc, (even understanding "planned obsolescence"), the manufacturers were all playing the "beat the other guys" game, and so we got water cooling, multi valves per cylinder, balancer systems, trick suspension systems, and of course all the fooferall involved in electronics and fuel injection systems.
ALL of that means ADDED WEIGHT.
You simply cannot build a capable modern motorcycle at a price that will sell enough units to be profitable, without the beasties weighing more than the golden oldies.