There are some good ideas on this discussion, but I can’t help but ask: how fast do you want? I know that the launch and all its issues were troubled, but they took only a month to deliver a huge update. Four weeks.
I can’t grant for sure, since I’m not involved with the development of the game, but let’s wonder about it togheter on what is the process of addressing a demand, like a bug correction.
Search out what is the bug and a way to reproduce it. Generally achieved through player reports.
Fix the bug. This can vary in difficulty, but it’s safe to say that bigger issues demand bigger efforts on solution.
Playtest the fix. This will often loop back to the previous step, and also need to search for things such new precedents for bugs.
This can be a lot of work. And among those there are things like planning priority decisions, parallel works, issues that demand multiple skills (coding + sound design, e.g.), investment on new content and many others.
Taking that in account, I find a montlhy update rate pretty fine, to be honest.
Also, having updates coming in smaller chunks and faster rates could be very counterproductive, since the game is developed by a few studios, instead of a single one, and they need to coordenate their works — that alone is some work. And the process that I confabulated above can become messier and more stressfull too, since each step would run on a shorter deadline to be delivered.