Because Haiti did not report the large majority of their Covid deaths due to a lack of a functional government. Haiti does not report deaths for the majority of other diseases either -- all disease reporting in Haiti is spotty with records mainly coming from hospitals with foreign funding & staff (primarily Doctors Without Borders / Médecins Sans Frontières).
Fundamentally Haiti's healthcare system and reporting is in complete disarray and effectively non-functional -- which seeing the country effectively has no government should not surprise anyone.
Reports out of the Dominican Republic (next door) reveal that Haiti actually had a horrible Covid death rate -- far greater than the Dominican Republic.