I suppose you are indeed correct on it. And yes, you have left for 6 months without really saying anything; however, it would be understandable if you do not wish to state your reasons towards leaving. But this also tells us that saying goodbyes are simply a choice, and people are just as privileged to choose not to read the thread.
I have also previously stated that it does entirely depend on who makes it, and how they make it. Taking to difference from a person who is not so well known in the community, or probably just joined the forums to say a goodbye thread, it could easily be considered as a form towards gaining attention.
However, if it were someone who is a reputable individual in the community, (such as yourself. <3 ) they could easily make a choice whether they wish to make a status update, thread, or simply say nothing at all.
Potential reasons towards making a goodbye thread would be so they don't leave the community without confusing any members, or worry them. And the forumers have as much freedom to state their reasons as much as someone who has the freedom to choose whether they want to read it or not.
c: