Why Don't we Investigate Voter Fraud?

Every election cycle we hear about voter fraud. We hear about it from both sides of the aisle. On the left, they tend to accuse the right, through some convoluted conspiracy of illicit activities of racially-based voter suppression. On the right, the accusations tend to show evidence of attempts by the left to manipulate votes through intimidation, fraud, and outright bribery.
No matter which side of the acclaimed corruption concerns you, the simple fact is this. It tends to go grossly under-investigated.
I submit that this is not necessarily nefarious. It is a bug, not a feature. It is one of the two things that I have found disappointing in the Trump administration. To be clear, I have been incredibly happy with Donald Trump’s presidency outside of these two exceptions… the buttstock debacle and the failure to investigate voter fraud.
Over the last several weeks, James O’Keefe has released damning and compelling evidence of serious voter fraud implicating high-level democrats like Ilhan Omar, the biological ex-wife of a suspected immigration fraudster, and some low-level Republican candidates.