From 1983: THE MAKING OF RETURN OF THE JEDI.
As the book market has contracted, publishers seem to have tried to counter falling sales by making film/ TV tie-in books premium products: hefty, slipcase laden affairs packed full of photos, production art and the like. You can see the logic: sell less overall but make more money on each copy sold. The Marvel movies and TV show have certainly led the way in this area.
Look back to 1983 and ROTJ: this excellent (but, apparently, hard to find... this is the only copy I have ever seen) behind-the-scenes tome was just a bog-standard paperback. Nothing fancy, not terribly pricy and packed with oodles of information (presented, like the modern Making Of... Star Wars whoppers, in a production diary fashion).
The more high-end visual stuff did continue to appear of course... the market was robust enough to support several different Art Of... type books (the large colour tomes and the smaller black & white sketchbooks) and, of course, several tie-in magazines with more stills and behind-the-scenes coverage.