As always when it comes to conservatives, you can trace their behaviour back to projection and how they think everyone else is just like themselves.
They put personal faith into the person they support, and see any criticism of that person as a personal attack. And they assume everyone else does as well, so they honestly think talking negatively about Hunter Biden is a personal blow to democratic voters.
It's because conservatives have zero imagination. All they do is project their own crimes into their opponents assuming everyone is as evil and guilty as they are.
"Hunter Crime Family" is laughable when we have a literal ex president crime family. Accusations Hunter took foreign bribes is pathetic when it's almost certain the entire trump family is in Putin's pocket.
Same people who lose their mind over hunter ignore jared and Ivanka actually being hired into the white house, a crime, not filling out their sf86, a crime, and profiting off of what they knew from being in the white house.
Most people attacking hunter know he's irrelevant. The right loves staking an absurd position or threatening massive harm to extract concessions without giving up anything important.
I also suspect that some of this is to poison the well so it's harder for democrats to prosecute trumps kids for all their crimes.
Whataboutism is their only defense, even if what they claim is evidence doesn't hold up to scrutiny. If they don't double down on it, they have nothing at all.