I'm what ways could the failure to enforce conscription weaken Rome?

The economy of Rome was also suffering. Rome was importing goods from its colonies but wasn't exporting nearly as much. This created an imbalance of trade. The colonies were creating their own finished goods and no longer relied on Rome for them. New coins were then made out of lead and gold to devalue the currency. Merchants now charged more money because these new coins were not worth as much as the old ones. This created inflation, this problem plagued the empire until its fall.

The problem of succession also contributed to the fall of Rome. There was never a set system of succession. After the death of an emperor, generals competed with each other for power. Once someone gained power they didn't rule for long; someone often assassinated them. This weakened the authority of Rome; corruption was common and law was almost non-existent.