Someone else will need to reply "why" but re cruise ships this has been a regular turnaround at Southampton and the Nab anchorage. eg 3 in , 3 out regularly/ since virus. Destinations/arrivals given ... Channel cruise, World, local coastal,unknown port/coastal ..all meaning similar.
for next few days.
Also http://www.southamptonvts.co.uk/Live_Information/Shipping_Movements_and_Cruise_Ship_Schedule/Cruise_Ship_Schedule/ for cruise ships only
in/out . Some days 1 day turnaround, other times 3 days etc.