Question on prepositions and comparisons
Based only on the grammar, the sentence is ambiguous. Without a preposition, it can be interpreted as
More tourists travel to Disney World than the Louvre travels to Disney World.
(There's a word or phrase for this type of ambiguity, but I can't remember it -- can someone help me with a comment?).
However, grammar isn't everything. This interpretation makes no sense, since the Louvre can't travel, and even if it could, it's just a single object so no one would compare its number to a large group of people.
Conversely, it's well known that both Disney World and the Louvre are tourist destinations. So the parallel is recognized intuitively, and repeating the preposition "to" is not really necessary, it can be elided and will be understood.
In order to remove all elision, you'd have to repeat "travel" as well, e.g.
Every year, more tourists travel to Disney World than travel to the Louvre.