How and when did wargaming become preponderantly Fantasy and Sci-Fi vs Historical? Has there been any discussion about this I should read? What's the history here?

I'm interested in games design, and apparently my youtube algorhythm knows this because it suggested me a video by some dude who's big noise in warhammer painting on his thoughts about game design. Which was fairly solid up to a point, but that point was "yeah, but you get to make everything up". In other words, there was no discussion about the need to capture period equipment and tactics when writing.

Like everyone of a certain vintage, sure I played 2nd ed 40k and Necromunda, but I had also read all the Don Featherstone and Tony Bath Napoleonic, Ancient and WW2 rules because they were in the school and public library in the same way you saw "Military Modeling" magazine there to check out.

So, how did it come to be that the default entry position into "this thing of ours" ceased to be History and became Fantasy/Sci-Fi?