I don't see a problem with someone publishing a backlog of multiple books at once. 3 per day seems pretty reasonable. Maybe even something like 3 per day and at most 10 per month might work.

On the other hand though, say you've been writing a web novel that could be sliced up into 3 separate books or you just have 3 books that's only now getting released. You could release them over time or you could choose to have all 3 go up at once. Not to mention as a first act of defense, it's a reasonable action to make and is easily adjustable later on.

There's probably other reasons why someone would release more than one book at once that's completely understandable, especially when considering what technically counts as a "book" such as translations or a company publishing titles of multiple authors under one name,

Chuck Tingle was pumping out multiple a month before language models were a thing.

Unless they're short stories, or someone putting out a chapter at a time for cheap and then compiling them into collections later. Still 3 chapters a day is pretty extreme, maybe a chapter a day I could see if you have the work ethic of Stephen King.