It's probably because Bitcoin and Ethereum service the altcoin investing market by being the largest pairings by volume and we're seeing less trading right now because of soft market conditions. This is going to change soon, probably in 2018 as we see cross chain capabilities and moving away from Tether as a pegged coin by allowing smooth Fiat conversions. When this happens the transaction volumes for both Bitcoin and Ethereum will likely fall dramatically exposing how little they're actually used in their intended use cases, more specifically Bitcoin.