My guess is that her static probably hasn't downed T9 yet (or at least not in an efficient a manner she's comfortable with). She might even have several recordings of it, but needs to make time in her schedule to edit the video(s) to make a suitable guide.
As for her Mog Ex video, we're kind of lucky she even put one out. She hates the Good King Moggle Mog fight due to a bad first time experience (it's explained in one of her Q&A videos), but said that she would put out a video if there is enough of a demand for it (which there was).
She currently doesn't have a video for Gilgamesh (yet), but he's fairly easy to figure out without a video.
That means that his chat is in subscriber only mode. It's not uncommon for broadcasters to do that, usually in an effort to keep troll spam down. If you've got hundreds of viewers, it can be difficult for moderators to, well, moderate the spam. MANvsGame started going to sub-only about a year ago. He said he would reconsider it if he noticed a decline in viewership. So far, he's experienced the exact opposite, and has increased the number of viewers as well as subscribers.
The subscription fee is (usually) $4.99 a month. The partnered broadcaster gets X amount (they're contractually obligated NOT to say how much that amount is) while Twitch gets the rest. For older broadcasters such as MANvsGame, you get an add-free experience plus special emotes that you can use all over Twitch. Sadly, under the current partnered program, being a subscriber doesn't offer an add-free experience unless you pay the $9 for Turbo status (or use Ad-block).
That being said, there's nothing wrong with videos, and people releasing visual how-to guides, it's more of the people who demand that a video be watched first and the first time run must be done with absolute perfection. I've also seen people become verbally abusive because someone offered a different strategy to fighting the same boss than the one they use. They also insist that their method is the ONE TRUE METHOD to completing a fight/ dungeon.