Read the medical uses section of that page.

The immunity doesn’t last that long and people get it when they need it.

The only reason post exposure vaccination works, at all, is because of the long incubation time. Some people get exposed, think nothing of it, and the time to most effectively use the vaccine passes. Others may not readily have access to medical treatment.

Check out where humans die the most from it:

https://www.who.int/activities/improving-data-on-rabies/rabies-epidemiology-and-burden