A recent survey has shown that today, very few people learn a language

Premise :
40 years ago - People were twice as likely to learn a new language as they are today, even after the age of 50.
Today - Very few people learn a foreign language + Our linguistic skills have NOT deteriorated!

Conclusion: Being proficient in a foreign language is not as fascinating as it once was.

Prethink: The conclusion is based on the consideration that the reason for very few people learning a foreign language is solely that they are not keen to learn and not that people don't have the skill.
i.e. if it's NOT SKILL then it's KEENNESS to learn.
We must assume that there is no other factor for the reduced likelihood of people learning a foreign language.

Note: If the argument holds the structure : Conclusion = If it's NOT X, then it's Y
then,
We must assume that - X and Y are the only two possibilities i.e. Nothing else can happen.

A. Becoming proficient in another language is not as useful as it once was.
This choice brings another factor i.e. It's neither the SKILL nor the KEENNESS, but the LESSER USE, that very fewer people learn the foreign language.
Thus, giving an alternate reason, the choice weakens the conclusion
B. Due to low health standards, the retirement age 40 years ago was lower than it is today leaving people over 45 with more spare time to learn languages.
Retirement age (any age) does not contribute anything in the argument.
C. Today, people have focused careers and do not need to acquire the knowledge of another language.
Similar to choice A. This choice brings another factor i.e. It's neither the SKILL nor the KEENNESS, but the LESSER USE, that very fewer people learn the foreign language. Thus, giving an alternate reason, the choice weakens the conclusion.
D. Because 40 years ago international travel was less accessible, learning languages had more appeal than it does today.
More appeal = more fascination.
Thus, 40 years ago, people had more fascination towards learning languages.
i.e. Being proficient in a foreign language now is not as fascinating as it once was.
This is just "rephrasing" the conclusion.
We need to strengthen the conclusion by eliminating the likelihood of any other factor ( i.e. other than skill and keenness).
E. Despite the far-reaching economic and social changes that may have occurred in the past forty years, learning a second language still provides all the advantages it once did.
Let's say - learning a second language does NOT have much ADVANTAGE ( i.e. a third factor), we can question the conclusion that it's the fascination why very few people learn new language. Thus, we can weaken the conclusion.
Now negate the statement.
learning a second language does still HAVE the ADVANTAGE - This means,we are eliminating the chance of third factor and hence are more closer to the conclusion that if it's NOT SKILL then it's KEENNESS (fascination) to learn for which we see very few people learning foreign language.

IMO, choice E is the best.
But I did not like choice E much as it says "ALL the advantages" . Even if learning foreign language provides similar advantages (ALL is not required), it's alright.

IMO E