I would say it’s not mysterious at all, the cause is just undisclosed.
If Richard Nixon had taken a dollar extra in tax deductions for a resort home, the “press” and their mates on Capitol Hill in both parties would be overwhelming with sanctimonious denunciations of his “crookedness”. Biden steals millions, is bribed by foreign powers which affects US foreign policy, and the Dems and Senate Republicans (with a few exceptions like Rand Paul, Ted Cruz and Josh Hawley) remain deaf mutes dancing with the “press”.