It seems that Gygax often had many Players (up to 20) at a game session.
While I'm not going to rule out the possibility that there may have been a special session or three in which 20+ players were actually sitting in the same room with Gygax, I think this is arising from a fundamental misreading of "in any single campaign [...] the referee to player ratio should be about 1:20 or thereabouts".
He's talking about the total pool of players participating in the campaign world. He did not have the same group of players sitting down each week: You had different players participating in each session, rotating the other people they played with.
Many classic adventure modules said they were designed for 6+ PCs.
Note that the number of players does not necessarily equal the number of PCs.
And many people around here have claimed to have regularly played classic D&D with 6+ Players/PCs. (Personally, I never *regularly* had more than 6 Players at a time in my games; my average was probably 4 Players.)
Whereas I don't think I've had a regular campaign with less than 5 players since elementary school. (And back then we each ran 3 PCs, so there were still 12 PCs on the adventures.)
I've recently been playing in an OD&D campaign centered on the Caverns of Thracia. The DM has had 20+ players participate (with probably about half that number attending more than 2 sessions). Although the single largest session had 11 players, most have featured 5-8.
(The session with 11 players probably had something close to 20 characters involved.)
Why, then, do all the examples of play, and advertisements for the game show only 2 to 4 Players?
That's probably a matter of clarity and photo composition. Not to mention expense when it comes to hiring talent for the photo shoots.
Was it just because showing 10 Players at a table looked cluttered for an ad? Or was there some other considerations? And if 10 people in a photograph is cluttered, aren’t 10 people around a kitchen table cluttered?
And if following 10 Players in an example of play is too confusing, aren't following 10 Players at the table too confusing?
I'm not really following the connection you're drawing here. The fact that introducing you to 9 different people in an example of play that runs for 500-1000 words is cumbersome and unnecessary doesn't seem to have any relationship to the effectiveness of nine people playing together.
It just seems like a real disconnect between what the advertisements for the game showed and what the publications for the game said was expected.
Next you'll be telling me that women on their periods don't spend their days dancing in all-white clothing through spring-time meadows filled with flowers.
I wonder, did anyone get into D&D gaming *because* of an ad or commercial? I've never heard anyone say they looked into the game after seeing an ad/commercial.
I became aware of the whole concept of "roleplaying games" through ads in comics. It then took me months/years to finally track down a BECMI Basic Set. (After being baffled by the impenetrable rulebooks of MERP, Bunnies & Burrows, and Batman: The Roleplaying Game.)
Of course, I was 10 at the time.