Who said they were going to join TW and Tacops? Last thing I'd expect, aside from a few select bits, like the arrow iv, VSPL, and handful of optional rules they put in BMM.
Starfinder is a bit over 500 pages, but it's a paizo corebook. splatbooks are 150 or so
Shadowrun 6 is ~300 pages, down from the monster 500 page 5th edition.
The pathfinder 2nd edition world guide (Lost omens) is about 150 pages, down from ~350 for the inner sea world guide a decade earlier
Pathfinder pocket editions are the same number of pages as their original printings, but softcover and 6.5"x8.5"; instead of 8.75"x11.25 and hardcover for the first editions.
Battlemech manual, ~150 pages. CampOps, ~200 pages.
Everyone's books are going on a diet. Sad fact of modern publishing, it isn't 2008, or even 2013, anymore.
This is, of course, logic, which is a notable way to be wrong with certainty. I don't
know what CGL is going to do.