I think that because the Catholic Church has taught that the Vulgate does not err in matters of doctrine.
Other translations such as the RSV-CE do err in matters of doctrine because they do not contain the Fullness of Truth–only part of the truth.
Can they be used? Of course.
If someone uses them exclusively and does not fully know the teaching of the Catholic Church could they be spirtually detrimental?
Yes!
As for medicine the RSV-CE is a medicine that can be used but does have doctrinal side effects.
Vulgate based translations do not have doctrinal side effects.
And the Catholic Church through its teaching can certainly give medicine such as the RSV-CE with its side effects because the magisterium’s teaching can correct itsw sideside effects.
The real comparison would be between a medicine with side effects and one with no side effects.
You wouldn’t win a case against a doctor because he gave you an approved medicine with side effects versus one without side effects.
You might enquire of the doctor if it would be better if you did in fact use the medicine with less side effects.
The doctor spoke at Trent and said to use the Vulgate
The doctor said it could be used in all disputations.
I trust that doctor far more than I do the Protestant “scholars” who came up with the RSV.