Well you are praying for someone who you will literally meet in the future (God willing). God can do anything but He doesn't always do anything. I'm sure there are many who pray for their future spouses, but still the divorce rate and bad marriage rate isn't any better... then there's people who just live their life serving God and they find the right person eventually. Who has the more faith? the person praying to God about their future spouse because they are worried about having a bad marriage, or the person who doesn't pray and trusts that God will provide.