Ethereum hashrate is down for a variety of reasons. The most likely reason is the recent Constantinople hard fork.
This hard fork changed the way how Ethereum miners are rewarded, and many miners decided to switch to other coins that still use the old reward system. Other potential reasons for the decrease in hashrate include the ongoing bear market and general interest in crypto mining.
Despite the drop in hashrate, Ethereum remains one of the most popular and widely used cryptocurrencies. It is still possible to mine Ethereum and earn a profit, although it may be more difficult than it was in the past.
For those looking to get into Ethereum mining, be sure to do your research and calculate whether or not it is still worth it before getting started.