Isn't that a poor way to come to that conclusion? This is a suicide forum. A lot of the people on here are people who have been struggling throughout most of their lives and have seen little improvement in their life quality and/or mental state. The thing is, the population of this forum is not necessarily a good representation of the general suicidal population.
Along with that, you also have to take into consideration the fact that a lot of members whose lives have started to get better and who have stopped having suicidal ideation often don't post about it. Many of them just stop posting or minimize their interactions with the forum without saying anything about it. Meanwhile, most people here who have noticed their life getting worse will make threads and posts venting about it. This can create the illusion that it doesn't get better, even though it can. It's just that you aren't as likely to see people whose situations have improved post on here compared to people whose situations have only gotten worse.
Something else that I would like to point out is that this whole "it gets better" and "it doesn't get better" stuff is dumb. In most cases, there are going to be periods where things do get better and periods where they don't. That is just how it is for most people. Some people may find that it only gets better or that it only gets worse, so even that it only stays the same, but for many, it varies throughout their life.