Obtaining a detailed map doesn't seem difficult. This is the same company that created Street View. E.g. SF has ~1000 miles of streets [1], that would only take 50 hours of paying for manual driving to map all of SF at 20mph.
Never said it was difficult but that their driving fleet relies on a lidar map of the region it serves. Its a definite trade-off so I would list it as a con but it does not mean one is better than the other.
1. https://data.sfgov.org/City-Infrastructure/Miles-Of-Streets/...