Nizze It's simple. Translators have to meet a certain speed as imposed by Webnovel. As a translator, I'd rather keep a massive stockpile to ensure I can meet that speed than to release more chapters for readers. I could mass release until all my stockpile is gone, and when I'm sick, I'll have to continue working just to meet the requirement. So why would I be releasing all that when I can keep a buffer and be at ease that I can take breaks?
For translator groups, they hire translators and also are required to meet even higher standards of release speeds. Their direct client is Webnovel, who pays them directly (but not necessarily by the SS earned directly), so keeping a stockpile is much more important. Translators and editors can quit at anytime and replacing them might take time. The stockpile is there to ensure that any transitions aren't disrupted. So as a translation group manager, I'll keep hundreds of chapters as a stockpile to ensure that I don't have to suffer pressure from halting releases because of this transition, both from readers AND Webnovel.
For instance, how long it takes to have a translator that reaches the standards and is agreeable to doing a particular work might take a few weeks. Then further negotiation with a translator for a book and signing them can take up to a week. And if the book is releasing as we speak, the stockpile is dwindling fast. 50 chapters for a female book runs out in less than 3 weeks. For a male book, less than 4 weeks. The workflow then needs to be set up, and slowly get into the groove of translating a new work. And that is IF a translator can be found. Different translators are suited for different kinds of stories, so you can't just move a translator over from another book either. And translators aren't just twiddling their thumbs sitting there waiting for books to do. If there's a spare translator, they will be assigned something. And even after they start work, they might not necessarily meet the speed requirements while possessing the quality standards as well. Then, perhaps another translator needs to be added, and the whole situation of finding another translator begins again. All this while releases maintain and the stockpile decreases.
If you actually check, Atlas Studios has raised quite a number of its female books from 14 to 21 chapters a week. And there are +3 chapters occasionally on TGIFs. Some of its male books are at 14 with occasional mass releases of +3. Some of the books that it has taken over from prior translators are eventually going to have their speeds raised to 14/week.
The determination of a mass release depends on how fast the translators/editors are doing, how big the stockpile is. If the translators hit exam period or real life issues and slow down, I'm going to be eating into that stockpile. If they are doing fast and everything is fine, I'll mass release. So it's ultimately still hard work on the translators' part to actually deliver a mass release. They need to go above and beyond what they are expected to do, and that deserves some gratefulness.