Wandering Adventure Party

Because the oral vaccine (in most cases) is a live vaccine that could cause a rare vaccine-associated polio. And the modern IPV can be administered along other intramuscular injected vaccines.
It is still highly effective and played a central role in eradication of the virus. It enabled mass immunisation efforts and also protected unvaccinated family members through vaccine viruses transmitted the fecal-oral route.
It’s still in use in poor countries with endemic polio.