I think that part of the reason the actual gameplay isn’t discussed is that–unlike the rules, setting, design, et cetera–it isn’t written down and thus easily transferable outside of the gaming troupe.

Roleplaying is not only a social endeavour in the actual playing, but in how it is learned. Most of us first learned by being brought into a gaming group. Those that lacked such had to give it a best guess as to the ‘right’ way to play. Early in the hobby’s history, it wasn’t too many steps of ‘x teaches y’ back until you get to someone who did not have other players as role models from which to learn. These isolated and autogenetic groups interacted only occasionally, such as at a convention or one person moving to a new town, and regional gaming characteristics began to emerge. Old & established groups can be hard to break into, not intentionally, but because they have been doing things a certain way for so long that it never occurs to anyone that there might be an alternative.

Secretly, many of us are scared that we aren’t ‘playing right’. If you have ever encountered any of the following situations with a new group or in a tournament, you probably understand what I’m talking about.
You are the only person without a miniature; everyone looks at you like you showed up without dice or a character
You are the only person with a miniature; everyone looks at you like you are playing the wrong game–or trying to show off
You are the only person with a Crown Royal dice bag; everyone else uses one of: ornate leather/silk/embroidered/chainmail bag, some sort of box with dice sorted by type (and high vs. low rollers, often), or the plastic tubes that the dice were originally purchased in
You are the only one who showed up in costume
You see someone rolling their dice oddly: from a Yahtzee cup, throwing it across the table, palm-rolling, just letting it drop, whatever
The troupe looks at you strange when you stand up & gesture when your character makes a speech
No body else actually talks as their character
Everybody else talks in-character, and can’t deal with your “My character tells them to surrender” or whatever it is your character is trying to say
Everybody else refers to their own characters in the third person (“Ragnar will now pick the lock”)
Everybody else refers to their own characters in the first person, and yours in the second (“I waste him with my crossbow! Laugh while you can, monkey boy”)
The look of horror when you reach for the book to reference something disputed during the game!

The above can all be big faux pas in one gaming troupe, and the obvious & only way to do things in another. Being isolated from the group–and in roleplaying this is a worse punishment than execution–is horribly frightening. No one wants to risk someone telling them that the way they game–often the only way one knows how–is wrong, and that incorrect gameplay is worse (and stranger) than showing up for game with your underwear on your head.