I'd take a broader picture view and summarize the general longer term HoloEN recline thus with various points (non-exhaustive, not sorted, feel free to add)
A large part of the viewerbase was never actually committed fans in the first place, but basically just lockdown tourists. Vtubers were at the time the fresh new thing to entertain them while they were bored stuck at home. Now both the lockdowns are gone and vtubers aren't fresh and new anymore, so these people have moved on. Arguably, besides making "number go down", this might not even be a bad thing, regarding the quality of the viewerbase?
For Myth specifically, when they came out they were basically the "only game in town" and audiences had no real alternatives. We don't count Niji's embarrassing first attempt at "EN" (India), and twitch indies were still a minor league wild west wasteland. Holomyth came at a perfect lightning in a bottle moment, being the first serious attempt at a proper EN branch and Hololive was already the most popular corpo for westerners at the time due to the run-up of viral JP sub clips etc.
This, coupled with the aforementioned lockdown buff, meant that HoloMyths numbers in the beginning were probably a bit overstated and didn't actually reflect their actual long-term realistic/"stable" popularity/viability. Case in point, Council came next and couldn't repeat the explosive growth, indicating it wasn't (just) about the qualities about the talents but also extraneous factors involved (lockdown buff, novelty hype, first-mover advantage, etc.). And nowadays, if you are a viewer that still likes vtubers (so not just an above lockdown tourist), but are bored or otherwise dissatisfied with HoloEN, you aren't captive anymore and have much more alternatives to watch and may find other vtubers that better suit your actual tastes.
For example, if you actually like male collabs, you can just go watch the original gendermixing company, Niji, where this is much less controversial. Or if you are in it for the coom and want more raunchier stuff and Holo has become too safe and boring for you, you can go watch twitch indies. Or if you liked the original general Hololive feel, but it has gotten too corporate and impersonal for you and you want a smaller more comfier and intimate atmosphere, you can go watch all the smallcorpos that kinda imitate the Hololive model more or less, but where you actually have a more reasonable chance to get your chat read and interact with the streamer.
The only reason to stick with HoloEN and disregard all the alternatives is a) you are happy customer who is actually satisfied with the product, b) you are a bubbled corpo-drone who knows nothing about vtubing beyond the blue dorito, c) you are a tribalfag with a "yeah HoloEN might be shit, but at least it's not as bad as all the other alternatives!" mindset or d) you are sticking around due to stockholm-syndroming yourself into a parasocial relationship with your particular oshi and think giving it up would be "betraying her". If none of those reasons apply to you, and you're open to shopping around for potentially better alternatives, you have probably dropped HoloEN already or at least don't just watch it exclusively anymore.
Also, a big part of the general HoloEN recline (long before males entered the picture already) was that too many talents feel like they have basically given up on any effort and just go through the motions, minmax and coast along on the brand buff. They aren't hungry and motivated anymore (some arguably never were - this is especially noticeable in the second gen who already knew that Hololive would be a golden ticket and you don't need to put in any effort), and it's hard to stay hungry and not become complacent when fans throw money at you no matter how much (or rather how little) you actually do and basically reward you for just existing. Unless you're especially driven, most talents would just succumb to laziness and no delivery. And for the few talents that don't, Covers retarded management buerocracy does the rest of destroying their motivation.
