It is difficult to bar civil cases based on the outcome of criminal cases or investigations because the standard of proof is much lower in the civil cases -- and for a good reason. Remember, being found "not guilty" or having the authorities decide not to prosecute doesn't mean "innocent" -- it just means that they couldn't get over the hump on being sure that what the person did was wrong. A criminal conviction can have lifelong effects, so the burden is higher.
We may not like it, and we certainly don't want to go through an ordeal like that twice -- but changing how the legal system has functioned (and again, sometimes for good reason) is always difficult. And with the clowns that we have in Dover, I am afraid every time that they start tinkering with laws.
Also, I have never understood Delaware's "defense of property" position. it's nice to see words on paper, but if you shoot someone stealing your lawn mower -- TNJ will launch a campaign against you, including rallies, until you are arrested.