You don't refer your friends for opportunities because you simply don't care. No excuses, you just don't care, that's all.
You've known them for how many years now? And you've not seen one business/career opportunity they could benefit from? You are playing the role of the devil, blocking God's blessings in the life of that person. Yes, you can refer people and they mess up, hopefully, they will learn and get better. And then you would have been a part of their growth.
One of the biggest advantages of linking people up with opportunities is that you would learn better how to spot yours too. It also help solidify relationships and expand your network.
When you block other people's blessings, you block yours too - albeit indirectly.
Program your mind to see opportunities in everything and everywhere, Even if it's not for you... that way, your ways is more prosperous and you live a happy life. Program your mind to be a blessing. Being a blessing is not always about giving people physical substance.
When you give someone a physical substance, you have helped one person, when you link them up with opportunities, you may have helped a whole generation.