Probably the biggest cause of death for Sperm Whales is getting hit by a boat and its propellers.

>Sperm whales (Physeter macrocephalus), currently listed as a vulnerable species, are severely impacted by ship strikes. Nearly 60% of sperm whales’ deaths are due to ship strikes in the Canary Islands.

https://www.frontiersin.org/articles/10.3389/fmars.2019.00379/full

The figures will vary by region but if a Sperm Whale doesn't get washed ashore. There's little way to know how it died or that it actually died. The other leading causes of death seem to be pollution, marine debris and malnutrition probably caused by us over fishing.