I can see clearly why this is. Publishers don't want to waste any whitespace if they can help it. Reducing the space between two sentences is one way of doing that. On a largish novel, the savings in pages could be quite a bit.
In my case, I went back to one of my novels I put into PDF format, reduced a working copy by eliminating two spaces after every paragraph, and redid a new PDF. The number of pages went from 441 pages to 422. Moneywise, that's quite a savings in paper if nothing else.
On the other hand, I've read a couple of novels on my wife's Kindle and have found that jamming sentences together on that tiny (for me) screen, really makes thing difficult to read. I wear trifocals, and my vision break point is about 12-14 inches away for reading. That means that the clearer the typeface/spacing is, the better for me.
If this is to become, or has in fact become, the new standard, then I'll have to go along with it - but I won't like it.
~Tom