The bitcoin, the news about bitcoin, any fake reviews about bitcoin an bad news related to the crypto. I think that they can be considered as strong reasons to create a lot of fear among all of the crypto holders. You can see that the fluctuation of ethereum has been following the bitcoin.
The price of Ethereum going down is surely not because of its slow network or high transaction fees. I fully agree with CuriousGeorge's reply. Ethereum or altcoins are down, not finding any support level is only because Bitcoin's price is getting lower every day. During 24 hours of a period- Bitcoin's price finds a support level and then getting lower than the support level in recent weeks. And with all the FUDs surrounding Bitcoin, other altcoins are sinking deep. But let's not forget that this market works just like this.