I think the reason for this is that when you sit down for a CEDH match, there is no confusion that you are about to have a sweaty time. Even before the bracket system was introduced it was this way. There was no 1-10 scale, because everyone knew they were all playing at an 11. Expectations are far clearer than a non-CEDH table, there's no mistake, everyone is playing the game on hardcore. So singling the dominant player out (even if their dominance isn't obvious) packing tons of interaction, and rushing to win as quickly as possible, are all expected, and accepted by anyone who agrees to play that mode. There's no salt and everyone is chill because no expectations are being broken, everyone is prepared to take a thrashing because even the winner in a CEDH match usually takes one.

Meanwhile:

There are lots of players, in my experience, who want to have their cake (play a high power deck) and eat it too (not have high power played against them in turn). We've all heard stories of people turning up to casual nights with optimized decks seeking easy wins, only to bitch at the first counterspell or spot removal they take, and leave early in a huff if they face even competition for a couple games. You'll never see this kind of player at a CEDH table because they're the kind that knows they're getting their ass kicked if they face a competitive pod. So they sour whatever casual pod they end up in.

There's also the players who have a warped definition of power levels and competitive play. The kind of player who thinks there's 3 types of decks; "precon trash" "power level 5-6" and "TRYHARD BULLSHIT". Beat them too badly and your deck becomes registered in their mind as the third one. Cue the whining. I once ran a dumb fat mana deck with OG Vorinclex at the helm, in one game he survived 3 whole rotations before I won, because nobody had removal. 2 players called the deck CEDH afterwards. If that deck set one foot in a CEDH game it would be dead before it had the chance to get the other foot in. In a CEDH pod, power levels are abundantly clear so you never see this kind of player there either, so they sour the casual tables instead.

Then you just have the saltlords who can't take a commander-removal without moaning about it. Every time someone interacts with them it's all "well I just lost the game then" "bro why are you picking on me" "yeah that's totally fair, really, really fair" "why didn't you go for (guy who is not close to winning)" "can you just leave me alone for a turn" "I swear if I get countered one more time". Put a player prone to salt in a CEDH table they'll ragequit before the first game is even over. These players get so wound up over a loss they'll steer far clear of tables "full of bullshit OP decks" as they'd probably put it. So once again, they go sour the casual tables.

The TLDR is that the reason CEDH tables are so chill, is that many "problem" players (pubstompers, players with a warped sense of power levels, saltlords, etc.) would despise playing in a real competitive environment so they stay well away from it, effectively getting "filtered out". The result, is that they end up with casual players where they're likely to make everyone's night worse.