In the US, for scifi, the SFWA requires a market to offer 8 cents a word or more, I believe, to be considered a "professional market" for the sake of counting towards membership criteria. That means most of the bigger scifi magazines are exactly at 8c (a very few above)
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.