My guess is they started planning and building the new headquarters before the decision to cease printing in Britain was made or perhaps even contemplated. They are making cutbacks at break-neck speed, and the impression they give is a rather hasty and chaotic retreat.
incidentally it's simply not true that ebooks are replacing physical books in society at large. Recent figures have shown decline in ebook sales and increase in physical book sales.
https://www.theguardian.com/commentisfree/2016/may/13/books-ebook-publishers-paper
https://www.theguardian.com/books/2017/apr/27/screen-fatigue-sees-uk-ebook-sales-plunge-17-as-readers-return-to-print
I think that the JW leadership is moving into ebooks and downloads simply because they can't make money from physical books any more. This is a consideration that is peculiar to JWs in particular, and not general to the publishing industry. It's not because books in general are in decline (they are not) but because the Watchtower organisation has been unable to charge a set price for the literature since the 1990s.
So new technology is not forcing the JW leadership out of publishing. Rather new technology is enabling JWs to get out of publishing altogether which was already no longer lucrative for the organisation for at least a couple of decades now. The signs that publishing was simply no longer generating money have been there since the 1990s: when they stopped printing attractive hardbacks and producing cheap paperbacks instead.
If they were still charging for the literature they'd still be making money out of them and they wouldn't be cutting back.
I would not be surprised if the organisation stops printing altogether. It may still want to print Bibles, tracts and a few select items. But they could probably pay outside companies to do that, as they did in the early years of the Watch Tower.
All of which does rather raise the question what bethel and headquarters are for. Other than to provide a nice environment for the GB to live and exercise authority.
Plus if they stop printing operations then what are they asking ordinary JWs to donate money for? To maintain JW broadcasting and the website? It's a bit thin grounds for asking monthly contributions from working people and old people to hand over life savings.