Because it's pop...
Arguably the goat head coach the man deserves anything that franchise has to offer, there are not many consistently kept a team in the title contending for 20 years.
If you went through 20 year dynasty with Kerr I'm sure you'd leave well enough alone.
Pop leaves when Pop says it's time he's earnt that.
Many Warrior fans already want to get rid of Kerr less than 18 months after winning a chip.