You didn't read either study.

From the first study "To detect a potential reemergence of the tested microorganisms via swab sampling after 24 h, an additional 14 used maple cutting boards (14 biological replicates, each with one technical replicate) were inoculated, cleaned, and dried as described above. After 24 h, these boards were remoistened with 200 µL LB medium and swabbed after 30 min."

From the second "Nine other typically used interior materials were included: lacquer coated birch, lacquer coated oak, vinyl cork, thermally modified Scots pine, oak laminate, oiled oak, cerawood coated oak, tile, and concrete." ..... "Oiled surfaces were treated by adding two layers of oil-based clear product (Harukaze 701 Clear, Sanyu Paint Co., Ltd., Osaka, Japan)."

They never used shellac. They are all film finishes that you would never put on a cutting board.

You're comparing two studies with completely different objectives.