Writing up one's research would be much harder if it wasn't for local history books to explain what conditions our ancestors were facing and what may have influenced their decisions. These books bring to us the neighbours, the local council activities, road boards and the influence of central government.
And best of all, they sometimes detail our ancestors activities in the district. The authors go to great lengths to make it interesting, finding photographs of people and activities from well known local historians who can't help their gathering habits and are willing to hand it on, knowing the respect it brings to their beloved district. The authors comb the archives and libraries then spend many hours checking facts and writing. And we get this bounty for a song. I doubt they make much money at it.
I haven't done a survey but have noticed that indexing was not a strong point with many of the authors, they either leave it out entirely or apply a slap-dash system to it. Some have done a very good job of it.
Indexing is an art so I've read and these artists are in demand. An index is not covered by copy-write, or so I'm told, so it is possible to publish one for these books of which we are not the authors.
Is it pie in the sky to wish for a central index of all these wonderful books so that family historians can identify which books to read? It would a mountain of a task. But first we would need the training to be able to do it.