What I can not understand is why on earth any serious business person would want to spend effort and time on Fakebook fanpage likes

The reason is simple - coverage. More likes you get - more people see your posts in Fb feed. More people read your posts - more $$$ you can get (selling your goods/services or just posting some advertising).

Moreover, as soon as Steemit will grow up enough to be interesting for big players - we will see tons of advertising and sponsorship packages. I'm sure