The uptick in popularity of the gun turn-in events, also known by the Orwellian term "buyback" is driven by the immense amount of money created by the Biden administration. Create trillions of dollars out of thin air, and bestow it on your political allies. They have to find ways to burn through it.
Gun turn in events or "buybacks" are one of the ways that money is being wasted. There are multitudinous others which do not get as much attention.