Because those who are "closer to me", "they've hurt me", and we have this kind of, "errhh I love them so much, why won't they do everything I want them to do, huh?" and we have attachment to them. Because we're so attached, we have a love/hate relationship.
The stranger on the street; we don't hate them, we don't know them, they're just another person out there on the street. "Oh, yes, I can wish it to him, I can wish it to her". Yes, "him" and "her", as long as they're "out there" and they're not so close to me.
This is why it's often harder. And who's the hardest person to have Compassion for? Yourself, right? You have a super love/hate relationship with yourself. It's been going on for many, many years. What have we got here? (in the hall)... from 59 down to about 28 - yes, it's been going on for many years. This is just it, that's why it's harder. But just because it's harder, doesn't mean it's impossible, and this is where we want to open it up. This is another reason why we want to have the Compassion/Lovingkindness wish exactly the same. Then it feels universal. When you do it for the strangers, and then you move over to someone close, can you keep the same feeling? Because the words are exactly the same, then you can test the feeling. You can test the mental feeling, which is what I'm really taking about, your attitude of the mind.
The way you give the wish is another way to test this. Do a lot of strangers for a while, "May so'n'so, so'n'so find Peace of Mind." "May so'n'so, so'n'so find Peace of Mind.", and then try yourself, real quick, right at the end! It may not flow exactly the same easy way as before. Try somebody you don't like at the end, whooh!, then it's even harder. "May, ahem, so-'n'-so so-'n'-so, ahem-hhhem, find Peace of Mind." In-out, y'know. In that wishing of the phrase itself, you can often see your attitude to the people involved, and that's another reason why we keep the phrase the same, so that hopefully, in the end when we wish, it's the same wish for everyone; it's the same wish for her: for him; and it's the same wish for me, too.