NOAA Fisheries provides the following list of known causes, and there can be more than one factor - for instance a whale may become deafened by noise and then get injured by a ship strike, or be unable to find food.
• Infectious disease, including parasite infestation
• Starvation (e.g., associated with El Niño events)
• Pollution exposure
• Trauma (e.g., injuries from ship strikes or fishery entanglements)
• Sound (human-generated or natural) [Including sonar and seismic surveys]
• Harmful algal blooms and associated biotoxins
• Unusual weather or oceanographic events
• ingestion of marine debris
Stranding causes
in different regions
in the US
(Includes all species of  marine mammals)