It's been proven time and again that solicitation strategies never become outdated.
After the nuns demonstrated the miracles in front of everyone, those civilians who had been clamoring to leave the Oasis earlier that day changed their minds.
Especially when they mentioned that it was the Oasis government issuing the recruitment, not the Brotherhood, the majority were moved.
The Brotherhood had a notorious reputation, and joining them meant completely abandoning one's conscience.
However, the government's army was different; the local garrison had a formal organization recognized by all the Covenant Nations. In times of peace, it was a coveted secure job. If a family had a member in the military, the neighborhood hoodlums who followed the Brotherhood would no longer trouble them.
In nonwar periods, joining the local garrison was extremely stringent. Each year's recruitment was practically monopolized by those with connections, and ordinary civilians never had a chance.