Also because so many Republicans are running on a platform of Pres. Biden being complicit in his son's shady business dealings. As the evidence on that has gotten thinner and thinner, they are clinging to the gun charge to retain credibility with their voter base. They are trying to say "See?! He is a criminal just like we said, therefore we were right and the president is trying to protect him. That means he's should be impeached, just like they impeached Trump!"