Right now there is little reason to aim for higher levels unless you want to clear an objective.
The fastest way to earn Idols is to reset when you've earned around 15.
Any time you spent for getting more Idols is kind of wasted.
Later This takes less than an hour, so the game is not what I'd call an idle game anymore.
There needs to be some bonus for reaching higher levels, like a multiplier for Idols earned for example.
We put in some fixes for achievements today. If it keeps happening, put in a ticket using the "Help and Support" link in the footer and we can take a look.
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Thanks for the feedback. We are looking into possible incentives for deeper runs.