Carpets also trap food particles and drink spills, so there's likely a hard-to-remove layer of decaying food particles in the carpet, especially if there are kids in the house. With hardwood floors, a robot can run around and pick all that up.

“PM10, PM2.5, PM1, and PM0.1 resuspension due to human walking” https://pubmed.ncbi.nlm.nih.gov/35463201/