Note the order in which he's announced the finalists:
Astrophotography, 13 pages of entries; Underwater, 16 pages of entries were the first two, and so on.
And the 5 that are left?
Street, 75 pages; B+W, 82 pages; Wildlife, 109 pages; People, 134 pages; Landscape, 171 pages (coincidentally, almost all categories I didn't bother with, too much competition)
There's more entries in Landscape than in Astro, U/Water, C/Lighting, Macro, and Abstract all together (presuming they're all valid entries, of course).
I think there's going to be a fair gap until we see the last of these finalists, it's an absolutely massive undertaking...