because Mexican American soldiers had far more casualties and far more service than any other minority in both wars. They believed that by fighting in these wars they would return to the US and become first class citizens...they returned with Purple Hearts and other awards, but were still picking cotton and other agricultural needs.
See, Mexican Americans were not recognized as an ethnic group in the US and were considered Caucasian, but when they asked for equal protection and right under the law they were not considered Caucasian. They eventually appealed to th eSupreme Court and a week after the NAACP fought their Brown v Board case, Gus Garcia fought for the US to identify Mexican Americans as an ethnic group within the US.
He won and the rest is history.