The reason that over 170 people were banned for the same thing is because Riot bans for cheats, hacks, third party programs, and basically any sort of ToS violation involving gameplay in waves. It makes it harder for the hackers/cheaters/programmers to figure out exactly when Riot caught them, so that it's harder for them to know exactly how Riot caught them.
Given the recent things that happened with Xerath, it's not surprising at all that there was a cheating ban wave. They probably lumped those cheats in with a few others that they had been working on, and rolled all the bans out at once. These sorts of bans do NOT have to happen right when they are caught. It can happen weeks, probably even months after it's detected.
And after months of posting here on the Boards, I can tell you... there are always going to be people posting saying "I didn't do it." Some of the sad, sad stories we get about how players weren't toxic, and never said anything at all in chat are just heartbreaking. Until one of the Reds comes in and drops the real logs and shows just how much they were lying. Which is why most of us now view things with a smidgen of skepticism, and look for the evidence.
If you have actual evidence that proves you haven't cheated in any way, we'd be more than happy to look at it, but I have to be honest with you. Someone who is your personal friend, looking at your computer and saying that you don't have a cheat on there is not evidence. Most teens and young adults (which makes up the majority of the playerbase) would consider it their duty as a friend to stand up for their friend and try to have them exonerated, even if it meant lying. And because there is so much potential for falsity in statements, we tend to look at the objective facts.