> it's so ironic that people would have fallen prey to a disease that is so easily mitigated.

Actually the root cause was not discovered easily due to a number of confounders. In fact it was discovered, then forgotten due to confounders, then eventually "properly" discovered again.

I can't remember the source, but I read somewhere that certain types of plants don't have the necessary vitamin C to protect you, so when ships were loaded with the wrong plant, people thought it must not be that. They spent their time looking at other potential causes before someone narrowed it down.