Perhaps in the 70s people also stuck to the general trend of female names ending with a vowel while make names typically ended with a consonant. Immigration from cultures such as India where this isn't the trend might indeed be responsible for it waning.
This has absolutely been the trend in India. Majority of male names from my generation and my parents' generation end in consonants, and ending with a vowel was indicative of a feminine name.
So I doubt Indian immigration at least impacted this trend in the direction suggested.
