In the sentence "Leurs métiers sont très difficles mais leur engagement est admirable" why is it not "leurs engagements sont admirables?

This is not different to English - 'Their jobs are very difficult but their engagement is admirable'. The sentence you suggest is grammatically correct but different - there is no reason that the first part of the sentence needs to have number agreement with the second, as there are 2 different subjects - jobs and engagement.

may be because the rules of french are followed...DUH!!

jobs is plural and engagement is singular

because metiers is plural but engagement is sigulier

Même problème