Well there are a few reasons. The first one is that anyone who does, or would, help you is doing it for free and giving up their own time. Please keep that in mind.
Also, there are many other members who are doing the same and asking for the same help.
You are doing the right thing by helping others, but please be patient. Demanding why people don't help you (for free) looks really, really uncool.
A couple of your texts are simply too long. If this is in preparation for an English certificate (IELTS?), then some texts are too long even for that. Keep the word-limits in mind, because you would lose marks simply for writing too much. On top of that, a long text with a "normal" amount of errors becomes tiresome to correct.
Another member, Jeff, wrote a great post on this dilemma several years ago. It's worth thinking about: http://www.italki.com/entry/136663