Bitcoin transaction fees will remain high as long as there are abnormal rates of transactions. The reason why the transaction fee increases when a vulnerable transaction starts is because the transaction with the highest free will be confirmed first. That's because the block always gives the highest priority to the one with the highest transaction free. In this case, many are willing to pay high fees to complete the transaction quickly, due to which everyone is demanding high fees. And thus the transaction fees only keep on increasing. Again, when the transaction volume returns to normal, the free comes down again
The miner chose the transactions to be include in a block, not the block automatically chose the transactions that has highest fee. Most miners choose transactions that has a high fee because they can earn more money than the transactions that has middle or low fee.
High transaction volume not necessary make the fee went high, if every people are make transactions by paying 1 sat/vbyte, it's won't increased to 2 sat/vbyte.