Does anybody know how O'Reilly chooses topics to publish?

For some reason, I don't see how it can be based on demand.

The reason, I ask, is because they haven't published a Delphi book in almost 12 years and Object Pascal is at least as esoteric as Erlang and as practical as PHP and as robust as C++.

So, maybe someone knows what rationale is behind O'Reilly's publishing methodology or what it is supposed to tell us about the relative popularity or usefulness of any given language or programming technique?

Oh, I forgot about pig and robotlegs