Many confuse casual games with simple games. Casual games permit the satisfaction of instinctual needs in small (2–5 minute) play sessions. However, many hardcore players of these casual games can play them for hours. In fact, they are the players who actually maintain the business.
I’ve worked on a bunch of them, and I feel like a clockmaker. They may feel simple, but they are deep: you move one gear and you must check all the others connected to it. You need patience to achieve the sweet spot (the perfect balance).
To properly study your competitors, you need to analyze them in immense detail. You may even need to record a session and review it frame-by-frame to fully understand the game’s circuit and how it works.