A lot of us that are deep into this space already see all the nuances, but there's a fat tail of people out there who are only just warming up to the idea that Bitcoin is not a scam. They're not quite ready to make the jump to Ethereum and smart contracts. Admittedly, most of these folks are the older generation that are not "digitally native" (i.e. millennials and younger).
"Bitcoin" conjures a physical, visual image. That golden coin image with the "B" logo. Ethereum has chosen, for better or worse, a more ethereal representation for itself that I think is tougher for people to grasp.
Remember when the internet was such a new concept that no one knew how to describe it? What did they call it? An information superhighway. Bitcoin achieves this in its brand name. At any rate, that's my theory for why it sticks so much better than Ethereum, and it's harder for people to remember ETH the first time they hear it than Bitcoin.