Looking at YCharts data, the average transaction fee for Bitcoin dropped 57.97%! While the reason behind the transaction fee decrease is open to interpretation, some experts are pointing to the Bitcoin Lightning Network, (System where transactions are made off the blockchain) as part of the reason.
A fee is charged for each transaction on the Bitcoin network. The fee is divided between the miners who secure the transaction. When the network is clogged and the demand for transactions rises, so too do the fees. The lightning network is a way to avoid clogging up the network by utilizing off chain transactions that later are put on chain when the network is less clogged.