Maybe the Biden administration has concluded that it's possible there may have been a lab leak. It would be damaging to them if they did nothing and ended up unable to conclusively prove there was no lab leak, because Trump has been banging on that drum for a long time now.
So, they don't really have much choice in this. They have to convincingly look like they're pushing to find the truth, or they'd be handing ammunition to the Trumpists.