While I fully reject basically all popular election conspiracies, there is one I firmly cling to. It comes in three parts:
Hanson’s Hanlon’s Razor - elections are run by state governments where bad incentives help facilitate incompetence. There should be a strong presumption that this will tend to be a poorly functioning enterprise.
Tragedy of the Commons - relatedly since nobody owns the process, it is destined to yield bad results. These results can benefit powerful interests, but these interests are not aligned with the objectives of efficiency, transparency, and consistent outcomes.
Cronyistic Control - the two parties (two-in-one we might say) have strong reasons to have a murky, doubt-filled election process(es). It can help drive their own get-out-the-vote message. It gives them room to maneuver both leading up to a contest where they maximize their own chances as well as coverage after the fact when they do poorly. In short the mess we get is a feature for them.
Thus, there are two facets to the conspiracy: One is undirected and emergent while the other is more deliberate although indirectly.
We should not be surprised at the inefficiency. It is actually surprising it works as well as it does—a testament to the honest, hard work of so many volunteers and government election employees. These true believers keep the ship afloat despite it constantly taking on water. Obviously the threat of everything from embarrassment to prosecution plays a role as well.
Notice too that the cronies have a vested interest in the system running well enough. As they stoke the flames of election fraud and other accusatory claims, they risk getting a solution they might not want—a well-run, transparent process that everyone can have great faith in.
Relatedly, Walter Olsen's work has been spot on in both describing a better world for elections as well as debunking the latest conspiracy theories about illegal immigrants voting.