It's a mistake to lump all magazines together and a bigger mistake to not read their website thoroughly. Many say why they pay low rates (they can't afford to pay more and many wish they could) and how long you can expect to wait for a response. Also, always consider that it's a good thing if it takes a long time as it can mean your story has made the final cut. My impression is that most magazine go through a system of instant rejection of stories that are either lousy stories or are wrong for their magazine. Then the rest get into the pile to be read and reread and finally, the problem of how many stories can a magazine print in a month? Let's say ten and there's a pile of 20 suitable stories. They have to finally reject half of them.
The editors I get maddest at are the ones who don't respond at all. Ok, rejection slips are a drag, but they are a kind of completion and an expected part of a writer's life; we have to live with them, like getting a cold and stuff. Editors who don't respond are rude +++.
I had lunch with a music mag editor early in my career and he had a lot of beefs with his freelance team. Mostly that they were picky: they didn't want to do this, they didn't want to do that - and when they did do it, they took forever. He then had to rewrite a lot of their copy because it was so crappy and they complained that he'd rewritten it. So I learned early on: always be available, be ready to write anything required however outside your comfort zone, and deliver quality work quickly. It's stood me in a good stead, because I'm the one that always gets called. That's non-fiction. As for fiction, the main gripes I've heard from editors is the amount of work they get that just isn't suitable because the writer has clearly never read the mag. That unusable slush pile is why the turn around time is very slow for fiction. For non-fiction there shouldn't really be any rejections, because you pitch ideas only, they commission the ones they want and as long as you deliver, it goes in on the date agreed.
...and you wonder why they don't pay you? Sorry, but honestly. You need to go get the qualifications and apply for the jobs these days; not many accept freelancers...that don't pick up the phone and ask first. Give them the heads up that a piece could be on the way to them IF they are interested.