Waymos do try to find somewhere to park too which has also been the subject of stories like this when the place they choose seems unusual. Neither types of taxis can always be parked since they may be in areas with little legal parking space available. Since there are incentives for drivers to be in busy areas where they might pick up customers it isn’t very uncommon for taxis in general.

Waymo behavior just stands out because the system isn’t concerned about how things look and there is more coordination/consistency. A human driver might choose a less efficient way to circle around in the area using congested roads etc. and every driver makes their independent and almost always different decisions. Waymos on the other hand can get allocated to the same area in anticipation of demand and then go to the same streets because the system deems those to be the best option available at the time.