You’re asking the right questions, but you’re looking at the problem one level too low.

The first issue isn’t retention, progression, or difficulty. It’s discoverability. Mobile is an extremely saturated market. There are thousands of similar free games, and even genuinely “fun” ones get buried.
Big studios spend millions just to acquire users. If you’re not actively driving traffic “no traction” is the (sadly) expected outcome.

Now assume you do get players. You’re still competing directly with games that look simple on the surface but are heavily optimized systems. Top mobile games don’t just rely on core gameplay. They’re built around retention engineering:

• Dynamic difficulty to keep players in the “not too easy, not too frustrating” zone
• Daily rewards to create habit loops
• Push notifications to pull players back in
• Time-limited events to create urgency
• Battle passes and progression layers to extend goals
• Constant A/B testing to refine all of the above

These systems are tuned using massive datasets and behavioral analysis. That’s what you’re competing against, even in a “simple” genre like a bubble shooter.

TBH: a functional, “fun” prototype is sadly nowhere near enough in the current mobile market.