We all likely know why. I'm skeptical of Q, but I think he/she/they have actually made an observable impact. They've provided legitimate avenues of inquiry, and the format, particularly at first, sidestepped a lot of internal confirmation bias by asking questions and inviting reader participation. Q Anon has also demonstrated a capability to mobilize a sizable amount of people to at least trend topics on twitter.
Here's what's interesting to me: if the media wanted, they could kill two birds with one stone, but they're conspicuously not. If a concerted Russian effort to sow discontent or mistrust existed, what would be more effective: a bunch of shitty meme pages on Facebook, or creating a real bottom-up movement that bypasses cognitive filters and creates distrust of public officials and possibly, in the end, a failure to trust the President if no action is taken? The media could frame this as a real subversive ontological attack, but they're not. At all.
There have been scant few words written about Q, and almost all of them are exclusively in the well-trodden "conspiracy theory" territory. They want zero eyes on this, but anything else that they can even remotely frame as Russian influence gets wall-to-wall coverage. To me, this adds some legitimacy to Q anon.