If you stop playing you'll miss out on something or be left behind and unable to catch up.
"If you don't log in, you aren't progressing anything. This means that your guild will fall behind, your arena rank will drop, and you will slow down the progress on fighting the world boss."
"1. There's a battle pass every month with 9 exclusive songs. These songs aren't purchasable afterwards for multiple seasons. 2. They add new songs to the base game in large batches. If you don't keep up in either way, you fall behind on the leaderboards or the grind towards Unlimited Play. 3. Some promotional songs have never returned to the game. (Permanent missables) 4. Unlimited play is a limited time pass. The timer starts ticking down as soon as it's purchased."
"Accasional special events, scheduled events, and large amounts of loot loss in return for a welcome back gift."