I agree.For me? It's about separation of responsibility, who controls what in that both DM and players have spheres of control.
Going all the way back to the "backstory" things, I'm not a big fan of the Players having Gotcha Rules. This is where the players have a rule they use to disrupt the game.
As a DM I have created a world, kingdom, town, land for the game.
And it is. And prep heavy DMs do it willingly, most often liking doing this labor. It does take time and effort. So the idea that a player just says "whatever" and does not appreciate it....well, that player can go find another game.THAT is what I meant by "prep-heavy", a game in which the creation of the setting is a laborious affair deserving of being appreciate
When the player uses a rule like "oh my character knows a guy and this happens as per the rules", it's disruptive. Suddenly it's, "well, ok, if the rules say so it must be so".
But few games, like 5E, back it up. they toss out one, nearly useless paragraph. And worse, a badly written paragraph. And it just stirs up more trouble then it is worth. The player jumps up, disrupts the game and says "As per The Rules, I say my character has an NPC Buddy right there!". And okay, a DM just nods. But then the DM has 100% control. So if the NPC Buddy says "oh sorry I'm busy" that is 100% allowed. Except the player won't be happy.
Prep Heavy games have always been an Unpopular Niche. This is always true with anything that takes time and effort.While I've never run prep heavy games if I understand what the term is supposed to mean, I also don't see why it matters or why anyone would feel the need to repeatedly make the claims that people who still support a style are just clinging to the past.
Anyone can grab some dice and do some random game play making it up on the fly. Only a few want to do heavy prep, and even fewer can do it.