Things are not the same
I don't know that I'm in any games with you, so this might be wildly inaccurate to your circumstance, but the instances I've come across that happening, the player gave so little information that it was either hard to figure out where they where/what they were doing, or the character was literally just sitting/standing there.
Now, like I said, I don't know if this is the case, but when it does happen, it's frustrating as a GM because I try to include everyone in the thread into whatever is going on. I've had information that I, as the GM, gave to players go entirely ignored as well, so I can fully appreciate your frustration when you've put something there to interact with, and it falls by the wayside.
I think all I can suggest on the matter is double checking your posts to make sure that isn't the case, and pming the GM if its a recurring problem to ask why/what they need from you for your posts to not be ignored.