Yeah, I don't get the concept of the skins either
So plastic tanks helped prevent the Ducati tank dent problem that happens when the bike tips and the handlebar bends. Bu then they started to bubble at the lower section, possibly from alcohol in the fuel.
This way you get to build an ugly but rugged tank (inside) and coat it in a candy shell. Mess it up and you only have to replace the shell (or half of it), which has to be less than the cost of a full new tank.
Why the vast color selection? Bad taste?
Scott