As far as experiences I've known in person and ones I've read online even, I've never seen any problems entering the US for anyone who's a dual citizen even if they left the US without presenting their US passport at any point (like my own experience mere months ago) but apparently this doesn't compute for a great many people.
There's one Reddit thread where I've bickered with someone who keeps advocating for using ESTA on one's EU passport to get to the US if someone can't use their US passport. And when I told him it's a terrible idea because this could subject them to scrutiny at the US border and be referred to secondary and kept there for hours, they insisted I put forth citations, which I couldn't because I don't recall the exact places I've read about the experiences. That person declared themselves "right" because of this . They also linked to several Reddit threads that alarmed me because almost everyone in those threads were encouraging taking this step with only one person warning against it but not giving sufficient details. I told the person to try doing that and report back to us.
So there's an alarming streak of people being paranoid about something that needs no paranoia AND a refusal to take common sense advice and common experiences as valid.
I've no clue why there's such a pushback. The airlines transmit APIS info to the US that the dual citizen is a US citizen even if the name on their boarding pass is different and this has been the experience for many people over and over without failure. It's as simple as that and it will be the same with ETIAS and ETA (UK).