luchog
Neo-Post-Retro-Revivalist
Because measles is a dangerous disease, especially in the very young. And there are often other issues triggered by the disease, all of which require up to date acute medical facilities to treat or support, it's a poor island they simply don't have the medical resources available.
On top of that, the measles virus causes what is known as "immune amnesia", resulting in susceptibility to other dangerous diseases that the victims may have been vaccinated against.
Measles vaccines protect against more than just measles. Here's how. Without vaccination, the highly contagious virus can allow other diseases to flourish in unsuspecting populations for more than two years after an infection.