^taunt parties
There are a lot of people in there who would rather not fight at all, and would rather goof off and fool around either doing stage specific glitches and tricks and basically showing off, to juts...well...really just goofing off.
Then there are of course the players who they see tactics they feel are "unfair or cheap" being used on another player(ice climbers chaingrab for instance) and feel, that for using those said tactics the player performing em needs to be ganged up on by everyone and make the match an annoying frustrating headache(of course sometimes the player is good enought o handle 3 noobs against em).
Then of course..there is just the simple fact that the majority of players playign it are NOT competitive players in any sense of the word, and actually like the items on, hate the fact that FD is the only stage ever chosen anymore in basic brawl, and really aren't interested in facing a competitive player, or even just pseudo competitive player with no items and the same stages all the time. You gotta remember Satan that a lot of people playing this game are still non-competitive and casuals, the majority of em don't find playing ti competitively fun, but rather find having items in a frantic FFA fun.
I personally don't really care much, and even out of basic brawl i'll face many folks with any ruleset(even coin matches) only thing i want to make clear when i face someone like this, is to remember that items promote far more luck than skill, and that many stages have such gamebreaking designs and exploits(stuff like temple, warioware, mario bros arcade etc) that can be used, that they really don't promote much skill either.
As long as my opponent(s) realize this, and are just there to not get super serious with the fighting i'm fine playing with the rulesets.