But if you're flooded with "hi" and the people don't have anything significant to say afterwards? I'm not a native English speaker but receive quite a lot of "hi" messages and for me it means "I haven't read your profile and I don't care what kind of person you are as long as you teach me English". In the beginning I replied to every single message and actually even now I often reply to "hi" messages with "Thanks for contacting me. Have you read my profile?" (which btw says that I'm not available for language exchange, random chat nor voice/video calls and that I'm not teaching English). I have a job, a family and I'm neither qualified nor interested in teaching others English. I hardly have time to practise my own target languages. I know I sound incredibly rude to you by saying this but on the other hand I do help a lot of language learners for free, I corrected several hundred German notebook entries. Please take into account that users here have lives outside of italki and that not responding to "hi" messages doesn't mean that they're rude and not willing to help others. I find it rude to not even care to read the profile and just expect that others teach them in return for nothing.

I don't think that the this could be actually the only and main reason. 

You as a tutor here on Italki, you probably get a lot of native speakers of English that pay you to have conversations, right? There are many spanish speaking people that would love to have a native english speaker to talk to, but why these english native speakers would prefer to pay someone when they have a lot of free opportunities? 

Everyday many Brazilians post here on the forums that they're looking for native english speakers, people with free time, people with true willing to help but they get zero responses yet a lot of portuguese tutors and teachers like me are being paid by native english speakers to have informal conversations. 

In my opinion is that people don't really know how to make a language exchange happen. Still the human being  in general lacks the knowledge of how to deal with another human being. Many people simply don't know what to talk to, how to organise the time, how to be productive during a conversation, how to come up with a topic to not let the conversation die after five minutes, how to engage the other one to continue talking and how to be interesting for the other person and vice versa. That's why people prefer paying tutors, because they don't have to share their time, let's face it, people have their moments of selfishness. When you are paying, you expect the tutor to organise everything and come up with the topics or to know how to lead the conversation. It's less stressful. 

Here is my personal experience. I'm not a native English speaker but I teach English here on italki. I'm learning Italian. A native Italian speaker got in touch with me shortly after I joined italki. He sent me a considerably long message in English (which must have taken him a tremendous amount of time to write) and the same message in Italian. This caught my interest. We agreed on a date and time and had our first Skype conversation. It turned out he'd bought a textbook just so he could help me with my Italian. I've been doing language exchange with him for a while now and he keeps emphasizing he really wants me to make progress. In return, I'm doing my best to help him improve his English. What I'm trying to say is:

1. He was willing to compromise and contact a non-native speaker.

2. He was willing to make an effort. He invested time and even money in this.

3. He has been acting selflessly from day one.

So to address the "hi" issue, there's nothing wrong with saying "hi" to people. But who in their right mind would choose a "hi" person over someone I just described?

@Miguel ELE (雷明): I know, and that comment was not meant for you actually. I was being sarcastic, yes, but in real life, if we go to someone and say "hi", just one "hi", not some super long self introduction or whatsoever, if that person doesn't hi back, we'll very likely consider them rude. But somehow you're taking the no response for granted and blaming the person who stood out to try first, for they did not try hard enough, just because there's more non-native English learners than native English speakers, who as you claimed benefit from their privilege.

And in a lot of ways some people hand over that privilege of selection to them cos they ONLY want to practice with native speakers. I've encountered people who are like "sure, you speak pretty well English, but I'd prefer to talk with a native." For these people, I could do nothing but wish them luck kissing native speakers' asses.

I personally take italki as a community where everyone could engage in language learning the way they want with enough respect for others' approach. In Chinese we have a saying, "人之患在好为人师", the trouble with some people is that they're way too fond of being someone else's preacher. If people want to start by just casually saying hi, then let them be.