"some random people send you email and have such "eclipse plug-in" problem" -> They are not random people, they are Ph.D. students working on their thesis and you can be assured that they will find a way to publish their comparison one way or the other. Some Ph.D. students will go at great length to figure out other's code before asking a question, but some will suck your energy big time and still do a poor job at representing your work. Now compare this to those who do not release their code: they can only be evaluated on their published results and they can spend their time on their next study/research work.
My point is that there is not a lot of incentive to release code: it requires a lot of your time, it is not always clear that granting agencies/employers consider this as being more positive than publications, and it exposes your work to all sorts of unfair replication/comparison.
Now, if research work without released code were never cited, that would be a terrific incentive to release your code :-)
P.S. I speak from experience and I release the code of my most important research work.
My point is that there is not a lot of incentive to release code: it requires a lot of your time, it is not always clear that granting agencies/employers consider this as being more positive than publications, and it exposes your work to all sorts of unfair replication/comparison.
Now, if research work without released code were never cited, that would be a terrific incentive to release your code :-)
P.S. I speak from experience and I release the code of my most important research work.