It wouldn't have been that hard to actually pass legislation and had an honest straightforward approach to handling getting rid of the penny. It would have been a popular move and easily gotten congressional votes (likely bipartisan votes).

I dunno. Apparently past legislative efforts have stalled out; wikipedia says it was a combination of lobbying from the zinc folks who have the business of supplying the penny blanks and some number of consumer advocacy groups worried about the cost of rounding up.

This is Trump's main MO, though. He finds things that people support (what his advocates sometimes label as 80/20 issues) and does them heedlessly in ways that violate process expectations of how a President is supposed to behave. His supporters love it, because he's ignoring the "rules" that let the 20% stop the 80% from acting. His critics loathe it, because those "rules" have value and importance and breaking them for an 80/20 issue also allow them to be ignored in 20/80 issues.