Due to new kingdoms keep coming in (with a new one likely a few weeks away), they also come with kingdom’s stat bonus, 2 from max level and 5 stars, one more if 10 stars become possible this year. That make players’ troop cards keep getting stronger, which also mean an alibity to take on more challenging difficulty as well.
It’s been a while since Warlord IV is added. The next difficulty level would be implement eventually. I didn’t think extra exp/gold/soul won’t affect the economy much as this point.