Their argument, repeated from the very moment that Biden was declared the winner and ever since, is that Trump's claims of fraud are "false" and "baseless."

But secrecy is normally at the core of fraud. While there might be isolated cases where, say, a person is caught voting twice, it's rare that massive fraud manifests itself immediately.  It usually takes an investigation to ferret it out.

Notice what happens if the logic of mainstream media, most of which was vehemently in favor of Biden's election, holds sway. If there is massive, sophisticated fraud, it is never discovered because there is never an investigation to determine whether there was fraud. The reason there is no investigation is because there is no evidence of fraud immediately after the election. But the only way to discover the existence of electoral fraud is to conduct an investigation, which isn't conducted because there is no evidence of fraud immediately after the election.

Let's assume, for example, that there was election software that corrupt officials were able to use to manufacture whatever number of votes Biden needed to win. How could anyone be expected to ferret out that fraud immediately after the election? One would need an investigation to discover fraud on that sophisticated level. But the mainstream media's argument is that there should be no investigation because there is no immediate evidence of the fraud. Thus, if the mainstream media's argument is accepted, the fraud succeeds because there is never an investigation into the matter.