Well, of course you're going to get more results doing it directly than you will on here. Real-Life and the Internet are two completely different things.
It's all based on knowing who you're talking too.
When you ask someone in real life, they can see you and hear you and from that they know you are who you are.
But when someone asks on the internet, all you get is a big blog of text. They don't know what you look like or what you sound like so therefore they can't really trust what you say. Simple.
And people do sometimes reply to invitations, but mainly if you're a girl.
This forum is, essentially, a Male-Dominated society (and I say that because of the sheer numbers, Karen! Don't worry, we know you're the most Dominant person on here. 😛). This means the majority of all Invitiations are given by Males, and there is a very small minority on here who are into the M/M scene. The only time you'll find a mass response to an invite is when a Woman sends the invitation. Go on, look it up. You'll see. XD
To put it briefly, invitations will rarely get replies if a male, like yourself, posts it.
If I came off strong in anyway or form during this post, I apologise. I have a tendancy to sound harsh in long messages. 😛