Comparison
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He visits his family less frequently than she does
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He speaks Spanish more frequently than I
In the first example why "does" is used after the pronoun she and why "do" is not used in the 2nd example...
Comparison
He visits his family less frequently than she does
He speaks Spanish more frequently than I
In the first example why "does" is used after the pronoun she and why "do" is not used in the 2nd example...
It's one and the same thing whether you keep or omit "does" and "do" in your chosen sentences. There is no deep reason behind why it was done in one case and not in the other. To not let others bat further eyelids, it is suggested that you keep them or leave them out in both the cases.
The answer is that if you elide (that is omit) the word "does" in the first sentence it becomes a little ambiguous. If you say "He visits his family more frequently than she" you could take it to mean that he visits his family more often than he visits her, in spite of the fact that 'she' is the nominative form of the pronoun and 'her' is the accusative. If you were to say "He speaks Spanish more than she" that would, grammatically, be quite correct.
Having said that the elided form generally is much less common now than it used to be and tends to sound pretentious when it is used. It would be unlikely that you would hear "He speaks Spanish more frequently than she" or "He visits his family more frequently than I" in normal conversation. You would be much more likely to hear "He speaks Spanish more frequently than she does" or "He visits his family more frequently than I do"
When you are speaking I'd forget about the elided forms altogether and say the verb aloud.
Both are correct; but "than me" would also be correct.