I would surmise it's more fear of wasting money and time on a plane (approx 13 - 16 hours at min cost of $2000 aud for a specific flight time,) only to be turned back at the US border.

I mostly agree with your sentiments, that not much has changed, there's been plenty of horror stories pre 2015 in regard to being pulled aside and sent back, misunderstandings perhaps but ...

Last couple of months I'd say there's a stark difference, there seems to be numerous media stores with a definite focus that it doesn't take much to be knocked back, and a few came down to simply having a record of being critical of Trump. eg. Alvin Gibbs (UK Subs) account of it which IMO sounds pretty straight up.[1]

Of course there's probably more than a few media beat ups where one would guess there's probably a bit more to the story but if so it's pretty quiet and perhaps perceived as an unwillingness for US authorities to comment.

[1] https://dorseteye.com/im-so-proud-to-be-deported-from-the-us...