Game developers like these aren't professionals, they're hobbyists. They're making games like its a hobby, not a professional job. They do no market research, experiments, etc. If you run a normal business or a normal startup like that, you will have similarly terrible results.
Be a professional. Look at the market. What monetizes well? What works? Hint: it's not the linked game.
Go look at the top grossing charts in the various app stores for an idea of what type of game you should be making.
I co-founded a small game company 2 years ago. We took 10 months to make our first game and have been releasing updates for it ever since. We're all working remotely. And, we're making enough money to pay ourselves a Bay Area salary.
I love video games. I love the game industry. I started as a QA tester and worked my way up from there. I will never do anything different. You can make money making games, but you can't be an indie game developer / hobbyist. Be a professional.