Very few genre magazines will accept more than 10k words. A handful will accept 20k-25k (Asimov's, Analog, Clarkesworld for example, last I checked). Many will prefer much shorter works.
And of course that is before taking into account the competition - the editor of a relatively minor scifi magazine mention on Twitter that their typical slush pile per issue was 1400-1500 stories.
I've submitted a couple of stories, but decided that effort vs. relatively low potential payoff was so low that since I wouldn't really be profitable when factoring in time spent anyway it was better to just put my stories on my website and pay to promote them to relevant twitter followers to pull in readers for my novel and increase my following at the same time.
The few short stories I've published so far has as a result reached a much wider audience than most of the main scifi magazines reach. E.g. even Analog was reportedly down to 27k readers by 2011.
But of course being able to afford to do that is a pretty privileged position to be in.
That's surprising; I subscribed to Asimov's for about 6 months back in 2015 and based on what I was reading, I assumed they must be publishing everything that comes in the door.
Also probably many people probably submit the same pieces over and over.
Btw if you find an outlet that seems to have no standards but also pays, the right thing to do is to stop being a subscriber and start being an author.
I assume editors don't get paid nearly enough.
I think they might be publishing stuff their core audience really likes, btw. It's just that audience is probably a niche.
Vonnegut had to convince at least two gatekeepers: his own agent and the editor at Colliers.
I spent a large chunk of time a few years back looking into the questions OP is asking, and the ultimate truth I came to is this: whether you're self publishing or going the traditional route, you're going to need some established gatekeepers to support you if you're going to make it.
In 1949, those gatekeepers were traditional publishers. In 2021, we still have traditional publishers, but we also have content curation algorithms, social media influencers, podcast hosts, and platforms like Substack and Patreon. If you can get any of them to put resources into promoting you, you'll have a real opportunity of making it - that is, if what you're offering is any good.
If you can't or don't want to get the attention of those gatekeepers, it doesn't matter how good your content is, no one will ever find you.
Also, would it not make sense to look at writing even from a more indirect point? For example, millions of people enjoyed the creativity of the /Friends/ writers, without actually reading a single word. Should they be counted as successful as a book writer with millions of readers?
Here's some other things he said on making a living as a writer: https://www.thenation.com/article/archive/vonnegut-writing-i...
Note that he got paid $750 for his first short story in 1949! I don't know how many places are paying first time authors that much today, and then you remember to calculate inflation.