I think the reasons that Riot ignores most threads on such topics is because the original poster:
1.) Feels they are entitled to something that they simply aren't. (i.e "I should be able to buy everything in 3 months with IP")
2.) Does not present a valid case in a polite manner. (i.e. "Riot is so greedy, all I want is...")
3.) Created a flavor of the week thread. (i.e. "Finale Funkeln needs to not be renamed.")
I'm sure I could come up with other reasons. At the end of the day, what can Riot say in response to these threads? "Yeah, we see your thread and have nothing to say on the matter at this time." Their silence says the exact same thing. If a topic is big and important enough, I'd expect a red to make a thread about it asking for input rather than trying to jump into one of the dozens of existing threads that are going to get pushed off the front page.
Don't get me wrong here though, I'm not defending Riot having not addressed some of these issues. While I might think IP income is reasonable, all new champs getting the same price creates a value disparity, does Riot really think Sejuani is worth as much as Zyra? The community sure doesn't and that's why champs like Sejuani and Lulu are hardly seen, they aren't worth the investment over other similar champs.