In answer to your question, “Why aren’t more being written?”–I suspect that these books don’t sell.
Yes, those like you who love them buy them enthusiastically. But there aren’t enough of those enthusiasts to make it worth it financially for most publishing companies.
And of course, writing an accurate book about a saint (which is what we all want to read) takes a lot of scholarly research. Not a project that an author will undertake knowing that it probably won’t get accepted by a publisher.
It’s too bad. But it’s reality.
One suggestion from me is that the publishing companies consider publishing well-written scholarly books about the saints as e-books. It’s a lot cheaper for them and for the readers, and then the information about the saints would be available. Of course, the publishing company still has to edit the book, and this is expensive and unless the e-book sells well, the publisher will still lose money on the project.
You see, it all comes down to bottom line.
Another suggestion is that publishing companies publish the well-written books about saints from modern authors KNOWING that they will lose money, but that they should make up for this by signing authors and projects that are sure-fire best sellers (e.g., books by Scott Hahn, or Catholic romance novels–yes, I think we need them!). That way, they would make money, just not on the saint books.