Publishers generally have a backlist of books that they think will take off, and they've got the printing sufficiently automated that they can do a short run, stock the wholesalers' warehouses, and wait. Shakespeare makes a good one. Just redo the cover every decade or so, and it has a bump in sales.
But then there are books which so perfectly don't fit when they are published, and so perfectly fit the situation 40 years later that...
The book is The Camp of the Saints by Jean Raspail
: a book only praised by the French and American conservatives, and therefore not worth reading. It stayed on the backlist, finding different republication rights in different decades, unitl 2011, when it hit the best seller list, and stayed close to it ever since.
Because it fits what is going on in Europe now, and what the political establishment wants to happen to the US now. They want a more biddable electorate, not as independent, not as well paid. And they're getting one.
And they're getting one.
And you wondered why Trump and Cruz had an impact.