And yet you're referring to flappy bird by name. Exactly how many flappy birds are there?
Most people who make games aren't trying to make connect3-like games, but rather something more fun/interesting. There isn't much point competing with medium to large studios that churn out games like candy crush anyway.
Stardew Valley, a 2D pixel art farming rpg-lite, was made over the course of ~4 years, by a solo developer who learned how to program in the process.
Undertale, a 2d pixel rpg-like, took ~2.7 years to make according to Toby Fox, the sole developer afaik.
Terraria 1.0, a 2d pixel art mining/building/fighting game, was made by a small team over ~4-5 months. After ~7 months, 1.1. After another ~9 months, 1.2. (They were big content updates).
Starbound, a 2d pixel art mining/building/fighting game, took ~1.5-2 years and launched in beta, with a small team.
Cuphead took 7 years with two brothers and a part time animator iirc, because they were absolute madmen and wanted to make a game with 60fps watercolor animation. Did they end up making a lot of money? probably, but that was quite the gamble.
Making games is tough when you consider it can require programming, storywriting, composing music, designing art, etc. And that's not including the business/marketing side. It -is- true that a lot of beginner indie devs spend way too much time polishing their games and end up not publishing them, but that doesn't mean compelling games are necessarily easy to make.
It seems to me that the parent comment blithely assumes most indie devs are trying to make games solely to earn income. A lot of indie devs are trying to make games they wish existed or just seem like a cool/fun idea that other people might be interested in, too. SWORDY is one such indie game that doesn't seem like it was thought up purely to earn cash, Gang Beasts* is another, and so on.
* Gang Beasts is actually made by Doublefine Studios but it sure feels like an indie game.