Why don't they explain why they have these restrictions? Their books are all in the public domain so what difference could it possibly make who downloads them?
The 24 hour download limit could possibly be defensible if they explained it -- for example they might encourage you to cache a copy of a book you'd like rather than refetch it every time. But they don't bother to explain.
I agree with coding4all: avoid this crap by simply going to the Internet Archive.
I suspect they just have a small amount of money and a large amount of load. You have to do something to try to keep load manageable while still serving the most users.
It's interesting to see one of my favorite sites doing this. There's always https://openlibrary.org/ which is ran by https://archive.org/ . I imagine Open Library has many of the same books.
The 24 hour download limit could possibly be defensible if they explained it -- for example they might encourage you to cache a copy of a book you'd like rather than refetch it every time. But they don't bother to explain.
I agree with coding4all: avoid this crap by simply going to the Internet Archive.