Ethereum popularity is due to the ERC20 tokens so everyone can create their own tokens using various ICO projects.
But the popularity is beginning to fade when there is a new generation of blockchain like Cardano and EOS and both coins both have the chance to become the next popular coin although it can not beat the dominance of bitcoin.
Remember that Ethereum itself is improving as well. Maybe popularity won't fade but will be even greater considering the announced improvements on this specific blockchain.