The F-16 requires specifically trained pilots to fly safely.
The Boeing in question was flown by pilots who were not trained for or even made aware of significant modifications to the plane's behavior.
A training wheel on a motorbike is not very hard to make well or drive with safely, but if you suddenly discover it during a sharp turn at speed, it's not going to go well.
Further to my comment above, here's the line from the Wikipedia entry, which I vaguely recalled:
The F-16 is the first production fighter aircraft intentionally designed to be slightly aerodynamically unstable, also known as "relaxed static stability" (RSS), to improve maneuverability.
1. The F-16 is the first production fighter aircraft intentionally designed to be slightly aerodynamically unstable, also known as "relaxed static stability" (RSS), to improve maneuverability.
Although the F-16 is from a different era. Perhaps we’re no longer capable of building complex systems?