The graph shows what happens when it takes more than an hour to find a block (around 03:00). Wallets keep competing for the highest fee, but none of that matters until a block gets mined.
Yesterday I paid 1.2 sat/byte instead of 1. That was enough to get on top of the large majority of waiting transactions, while my wallet was recommending to pay 80 times more. Even now, Mycelium recommends 82 sat/byte for a "Normal" 30 minutes transaction. For 2 hours, it recommends 59 sat/byte, and only for 3 hours it drops down to 8 sat/byte. It's such a waste of precious satoshis to follow the default fee, and on top of that it forces others to do the same.