Not being mean and the other things you mentioned are only the first step onto making friends. But it doesn't end there.
I see you frequently put yourself down. Is this normal for you to do in front of others? If so that could be one deterrent to making friends. Sure we may all have moments where we feel like thar, but if it is the norm for you people will avoid you.
Many simply don't want to be around such negativity for very long.
Some may see it as your fishing for compliments, which people dislike.
Others may come around believing they can help, and when they can't, they move on.
Your inability to come to a rational conclusion, and instead are convinced it's an IQ thing shows your inability to recognize and diagnose personal issues in a healthy and balanced manner.
This affects the way you approach and interact with people, likely in a negative way.
It also prohibits any real personal or social growth as your focus is in the wrong area.
You falsely believe that everyone that doesn't stick around does so because of a fault within you. This, again, negatively affects the way you approach and interact with people.
The reality is most of the people any of us will meet won't stick around. There are too many variables to get into why this is so, but it's pretty normal for everyone, not just you.
And this is especially true online. Most people aren't online to seek out long term, lasting friendships but for some generalized social interaction. It's true people can form friendships this way, but those are formed naturally and often unexpectedly.
Which brings us to the next point, the more you seek friends the more you're likely to push to become friends with people, and this will actually drive people away. They'll sense the major imbalance in the relationship, or feel pressured, and not want to continue.
Friendships form naturally based on connection, not forced by someone trying to fulfill a personal need.
And that touches on the likelihood that by now your motive for friendship is more about You and getting what you want than it is on two people sharing a mutual connection. And, again, this will affect the way you interact with and approach people. And in turn how they respond to you.
It may be possible you're lacking in some social skills that's making it harder for you to connect. And you may not be able to recognize that lack.
Or any of the issues mentioned (or something I haven't mentioned) above may be driving people away.
I used to have trouble holding onto friends. And I started down the "woe is me" path, much like you're doing.
But eventually I had stopped pitying myself and took a long hard look at myself, the way I behaved, spoke, etc...
And I began to consider some of the complaints about myself I heard from friends over the years. Especially ones that came up repeatedly.
As well as thinking about those same behaviors I saw in others and how they affected how I felt towards the people exhibiting them.
What I learned was some things I didn't believe mattered or affected my friendships actually Did affect them.
I began to see some negative traits I was unaware of that I exhibited towards my friends.
And as I began recognizing and accepting that these things were there and existed and I was responsible for, as well as seeing how they affected others, I also began to try to change them.
This meant treating my friends differently, speaking differently, being more patient, not always speaking so negatively (including about myself).
It wasn't easy, especially accepting and owning some of these behaviors I had spent many years denying. But I did improve, as did my relationships.
Now there's plenty for you to digest and consider. And not one piece of it has Anything to do with IQ.