Because they were absolutely events triggered by a parser. Now, without one that could have simply occurred a few runs later, or the very next, but the fact the advice arrived when it did because there was far less effort required on the part of the improving-player-to-be's party members to notice that a problem was occurring. Their knowledge wasn't the issue; their attention and sense of urgency was, and each was supplied at a single glance by a parser.
I have never once said or even implied that self-improvement is impossible without a parser. I have said that it is a helpful tool, however large or small its margin in the hands of various players.
I guess to put it another way, I fail to see how the harm you suggest, if even existent, outweighs the boon, however small you might find it.
Maybe our experiences with "epeen waving" have just varied tremendously, as I've yet to see it occur even once. (I've seen friendly competition between DPS. I've enjoyed the same myself. But I have never seen anyone boasting about their numbers outside of their raid group following a particularly DPS-solid attempt or clear.) I have, on the other hand been threatened to be reported multiple times because I've said as a tank, "my bad, our DPS isn't high enough for a pull of that size; I'll trim back" when breaking in a quickly learning healer, or especially if one of the DPS made light of said healer when the matter was out of his or her hands; survival revolved around at least a couple mobs dying before I ran out of every single CD, and no amount of mana-burning heal spam can make up for that if the mobs are dropping at half their DF-average speed.
Now, perhaps that is biasing me; I'd honestly prefer that people grow a pair and not take an objective inference or rational compromise as personal vindication against them by a player who, I'm sorry to say, probably is not invested enough in them as a specific person to get any enjoyment out of insulting them, and I think plain information would help in that regard. If I can't make them understand anything outside of their tunnel vision, I'd like to at least be able to say, "Given the healer and I's gear and CDs, we'd have needed about xxxx output, in my experience spamming this dungeon with various groups, to get through that. If you don't feel comfortable making up that difference, I'm going to cut back so we don't die, especially now that my CDs are down," and they would have that number in front of them, everything out on the table so to speak. That sounds very much like a positive, helpful, and toxicity-reductive change to me, based on my experiences.
Half the time it feels like there's this ambiguous void, or wall of passive confrontation, by anyone who staunchly feels like they might have something to lose if anyone did know how they were doing just based on the damn stereotype. I've yet to see "parser discrimation" in the sense of people being weeded out based on their numbers without so much as a offer of support. I've seen reverse aplenty, where anyone who expects basic competency must somehow be elitist and parsing. And the funny thing is, you're not going to kill that boggie-man by actually finding a way to remove parsers completely. You only get rid of that my pulling those afraid of it out of their closets. Oh look, those are my performance indexes. Hmm. I'll do with that what I will. Not some terrifying, morally bankrupt, infringing, and masturbatory tool, but just... information.
So what exactly is the harm you're assuming here? Because I truly cannot see how it outweighs the benefits, whether in terms of convenience, fairness, or community impact.