There are a lot of articles like this one that say probably, you can't make money from apps.
This is sort of true as an average, but you're not an average, you're a particular person. So it's important to figure out whether or not it's true for you.
The nature of building a multi-billion dollar industry very fast is that it has tremendous gravity. You get people from the web world, or the desktop world, who get pulled in to do a project or two. But even the best developers are going to do a bad job their first mobile app rodeo.
But the gravity well surrounding mobile apps doesn't just capture web developers. It also captures the sort of IT-plus-scripting-skillset that you find for $10/hr in countries you have no plans to visit. You'd be surprised at how much volume the $10/hr "programmers" do. Not just the projects that set out to hire $10/hr programmers (although that happens) but there's a tremendous industry of having a US-based sales team to find projects for your $10/hr programmers somewhere else, and you'd be surprised at how even Fortune 500s find themselves in their pull. Often the rabbit trail goes through multiple entities who subcontract the work to somebody else who subcontracts the work somewhere else... I won't name-and-shame anyone here, but you'd be surprised how often this sort of thing goes on.
There's a similar story with designers. They may have several years of web design experience but it's their first app rodeo, and of course that's going to go poorly. Or else you may end up with some "designer" who works for $10/hr and took a class on Photoshop once.
Finally, and possibly most surprisingly, there's the product people (or "decision makers"). A manager at, let's say, Disney, may be an expert in operating a theme park, or organizing a TV show, but that doens't mean they know anything about building a mobile app. And very often, the person who is brought in to manage a mobile project is somebody like that--a competent person in some other field, who's never made an app before, and not even the best technical and design teams can build a good mobile app out of a bad playbook.
Most mobile projects have one or more of these handicaps, and many of them have them all. But the third one is the deadliest. You can sometimes recover from a bad designer, you can rarely recover from a bad developer, but you can never recover from a bad manager that outranks both of them on the organizational tree.
The good news is, if you can address these problems, you're substantially, substantially ahead of the revenue statistics.
Another large category of apps are "bad ideas that somehow got funding". For example, if you're trying to write a game, that might be fun for you, but it's probably a bad idea commercially. If you're trying to do something that Apple isn't going to like (interfere with system apps for example, a common request) that's also a bad idea. If you're trying to do something that requires magical new technology that doesn't exist, that's probably also a bad idea (unless, of course, you're a researcher).
A good idea is one where you know your target market (a specific target market), you know what kind of product they want and you know how to reach them in volume. Even better if you already have reached them in volume and started testing how they respond to your product (yes, before it's built). Now you are light years ahead.
An easy way to turn $500/month from a failure into a success story is to only spend 1 day building it. A lot of the apps I work on for myself have the property that I can build them in a weekend. You stack 10 or so weekends together and now you're onto something.