Not arguing about the propaganda point, but there are legitimate reasons for not shooting down test missiles.
If you always shoot down test missiles, then NK just has to keep firing test missiles until they build one that doesn't get shot down.
If you always shoot down test missiles, then NK just has to keep firing test missiles until they build one that doesn't get shot down.
It's just not reliable enough to risk and as such is still a last resort measure.
Defending against a nuclear ICBM is not possible to do reliably. It's a sad reality.
As long as they don't rely on foreign supply for their missiles[1], they can manufacture them forever without having to pay anything to anybody.
[1]: it may sound like a bold hypothesis, but I doubt anyone would ship missile materials to North Korea. China could, of course, but that would be a bit risky diplomatically.
Historically, Iran, North Korea, and Pakistan cooperated on nuclear and missile tech, though I think that was engineering rather than parts.
And with NK slaves showing up in Polish shipyards, that is highly unlikely.