Vaccination rates are low in other countries, because the vaccines are not available. As simple as that. Being an Indian, I am trying hard to get myself vaccinated for the last 3 months. Unfortunately no slots are available, because the vaccines are in short supply.
Yes, vaccines are in short supply in most of countries right now but sooner or later that will end. And when it will end, countries where people will vaccine will have 70% population vaccinated (since kids can not be vaccinated that mean that there has to be 85%+ adults vaccinated to reach 70%). Others countries with have 50% or 40% people vaccinated. And that will be to little to prevent further spreading of covid. Those countries will suffer most on long term.