I'm going to speculate here.
The reason we're not seeing 3d signage any more is because of the difficulty and effort in adhering to the guidelines of double-fixing. I remember when I was reading through the coroner report for the RTRR and in it, engineers were pointing out fixings in the ride with single fixing points and that they should be addressed.
You can see such an example in the new sign in the image above, there's the chain holding the sign as originally but also there's now an additional wire as backup.
The incident DaptoFunlandGuy described at Wonderland is why. Something actually occurred, it was risk-assessed and now probably every insurance company for theme parks in Aus is going to require double-fixings or they'll have to pay additional premiums.
When you've got a 3d manufactured sign, how do you guarantee double wired fixings for each element stuck on the front without making it look like trash? Sure, you can glue/screw/bolt but a bean counter in insurance land somewhere will probably say not good enough.
There comes a point where a standard printed sign does the job well enough and is not worth the effort in fighting the bureaucrats.