I’d always assumed it was love of the new, but looking at the Tokyo Station renovation and many other brand new retro buildings in nearby Marunouchi is proof that it has nothing to do with style, let alone modern style. The station itself is a particularly extreme example, because they’ve knocked down the old domes that are everyone’s image of Tokyo Station and rebuilt the even older ones that no one missed or even remembered.
My new conclusion is that just renovating here and there isn’t gambarimasu (do your very best/ work yourself to death) enough. Alternatively, maybe Japanese decision making processes make a big decision like knocking the whole thing down the only way of getting projects properly underway. Or it could simply be bribes etc from the construction industry.