1: Control issues. Missing significant vertical stabilizers makes stability an issue along multiple axis.

2: Central engine placement causes issues with cargo. Not a huge deal if all you needed was under slung bomb bays and fuel tanks in the wings, but a significant issue if you need to fill the plane with people or parcels.

3: Maintenance. Current commercial airplanes have easy access to the engines for inspection and maintenance. It's relatively simple to take off an entire engine and just swap in another if needed when your engine is bolted to the underside of your wing. When it's built into the place chassis? Not so much.

4: $$$$$$. Flying wing designs are more expensive in production because you can't manufacture different sections of the plane separately and basically lego things together at the end. Development would be pricey. Testing would be pricey. Getting approval to take passengers would be pricey. Construction is pricey. Maintenance is pricey. About the only thing less expensive for a flying wing design compared to a conventional plane is the fuel.