Not sure why, other than the fact that I've been that one, but I'll chime in with my observation. To start with, I'm somewhat of a shy person, for whatever reason, and rarely introduce myself to those that I'm interested in. Quiet, observing life and human nature first and foremost, at the same time, searching for the ONE that stands out and leaves me awestruck. Very hard to find (or judge) from a self described post on some dating site, though I have seen a couple, and I may introduce myself soon enough. Back to the question....
I've been on a couple of these sites for about two months now, been hit on (?), and traded e-mails with a three different ladies who seemed interested. The unfortunate part I've found is this, these sites seem to be the stomping grounds of internet dating scammers. The conversations seem to go well for the first couple of e-mails, but afterwards the inconsistencies start to manifest themselves, it's all downhill from there. She's from (near)(my town)but is in Nigeria for the week. Or, her profile says Albany, but in reality you find, she lives in Chekzoveria, or G-d knows where! Or the fact that I ask simple questions that go completely unanswered. I'm very easily insulted when, after two e-mails, there's no real connection, yet they're addressing me as(Dearest)or(My Love), like I'm so lovelorn to buy that. Some actually do, (buy into it, that is)and get taken, (but not in a good way). Me? I don't like having my time wasted for me, and as soon as I figure out that game, I won't write back, and it's off to the dating scammers website I go to report my experience with so-and-so, in one of her fifty aliases. The only three women I've spoken with through these sites, and each one of them running their own scam, and casting the net(sic), far and wide for any takers. Can't speak for other men, but I'm no fool.
In some ways, I've found it to be an enlightening and humorous experience.
On the other hand, these experiences have left me a little gun shy about introducing myself, but I'm over it. Fortunately, no winners, no losers, just lessons learned.
By the way, I'm in no way implying that this actual circumstance applies to your situation, just relating as to why I've done that very thing before. Make any sense at all??

oh that definitely makes sense....that kind of situation is understandable to just stop talkin to someone...

are you talking about e-mails or on the phone or both?

I'm so confused.

Maybe they are busy working or antisocial!

both...i've only had one person do that on here..most of the guys that have done this i didn't even meet on here

well when it comes to e-mails guys will start to get bored with them unless you two have something extremely in common to talk about like if you are both artists or something...but sometimes the woman response to his e-mail may not contain anything worth responding back to so he may feel she is not interested in him or no longer interested ..so my advice to e-mails is to do your part to keep the conversation interesting if this do not work then you two at that point in time was not meant to be and you shouldn't take it personally

I myself am not much on conversation & some women on that I have talked to I've had to carry the conversation & they contacted me.... but again I'm not much for conversation...

i'm guilty of it. only once...

i just wasn't interested. didn't feel like writting anymore. i was going to write her to say something to that effect, but i just got busy and time went by. as time went by, i felt like it would be more awkward than good, so i just left it alone

funches has it right. If you are answering mail from them make sure you ask questions showing interest and make comments of something they said, or ask for clarification of something that was said, not in a nosey way but a curious way.

If the mails are just about how are you , fine, how are you, okay, whatcha doing, nothing, then it is doomed for failure. If this is not the problem then interest is not there anymore and better to just move on.

Hope that helps

Tag, your it. Just my theory, we are waiting for you to call...

Don't take it personal, especially online.

It happens to all of us but that is the world of internet dating. It even happens in real life.

Ending things with someone is a difficult conversation to have therefore many people just avoid it all together.

Please don't let it damage your self esteem. It usually has nothing to do with YOU.

It goes both ways. Maybe he thinks you have stopped talkin to him. Maybe he thinks you arent interested anymore.

well, if a girl doesn't show enough interest/initiative sometimes i forget all about her as more and more things in my life distract my attention, such as hobbies, schooling, other girls, etc.

As others have said...it happens unfortunately. You may be thinking it's going well but they may not. As much as I usually am honest & say I'm not inerested...there are times I have just stopped returning calls/texts/e-mails, because I wanted to avoid the confrontation. I'm not saying it's right, but people do it.