I mean, it really shouldn't make sense, because Bitcoin is a completely separate currency from ETH... but it's still way too deeply connected to 'anything crypto' in people's minds, it seems.
Not really anymore. If for example you look at the ETH markets, the top 12 trading pairs by volume are with national currencies, and the first market with ETH/BTC is down at the 13th spot.
Bitcoin is the de facto base currency for all cryptocurrency exchanges.