aim at doing vs aim to do

[Hoy-B]

When Medicare was enacted in 1965, it was aimed at the prevention of a catastrophic illness from financially destroying elderly patients.
A. at the prevention of a catastrophic illness from financially destroying elderly patients
B. at being a preventive against catastrophic illness financially destroying elderly patients
C. at preventing a catastrophic illness from financially destroying the elderly patient
D. to prevent a catastrophic illness financially destroying an elderly patient
E. to prevent elderly patients being financially destroyed by a catastrophic illness

Official Explanation
Verb Form; Diction
Two issues can be identified here: first, we must determine what form follows the phrase it was aimed, used to describe a goal or intended purpose; second, we must determine what preposition (if any) connects prevent or its cognates with the thing that is actually prevented.
A. This choice uses the idiomatically correct was aimed at. However, the word prevention incorrectly takes both the preposition of and the preposition from; this makes the sentence awkward and ambiguous. Furthermore, using the noun prevention makes the sentence wordier than choices using some form of the verb to prevent.
B. This choice uses the idiomatically correct was aimed at. However, using the noun a preventative makes the sentence wordier than cases using some form of the verb to prevent.
C. Correct. The phrase at preventing is correct in context: it describes Medicare's intended purpose. Furthermore, the preposition from correctly indicates a consequence that has been prevented.
D. This choice uses the idiomatically incorrect was aimed to. Furthermore, it fails to use the idiomatically correct prevent from.
E. This choice uses the idiomatically incorrect was aimed to. Furthermore, it fails to use the idiomatically correct prevent from.

OA said "aim at" is unidiomatic. Why? What is the difference between aim at doing vs aim to do? Can you please explain this? Thank you.

[esledge]

What is the source of this question? We can discuss the free Official practice test questions, but those don't have explanations, so I think this one might be from the OG (?), which we can't discuss for copyright reasons. Please let me know if it's from another source, and please see the Sticky note for posting policies if you have any questions. Thanks!