I remember the complaints that he wasn't proposing something specific before the election. So actually I don't think most people are aware that it is complicated. Otherwise they wouldn't have expected a simple solution.
The issue at hand is that Trump is either willfully or unknowingly ignoring that he and his people are the ones who actively prevented us from having a better system. And the only reason why they're only now acknowledging it's a hard problem, is that now they're the ones who have to fix it.
In my experience, especially in complicated situations people really crave for simple solutions.
The essence of the success of populist politicians is to say there are simple solutions for all problems. No hard choices are needed.
We can have it all.