Bookstores. Need to stock the FIRST of a series

More and more light fiction comes in series.  Once an author gets something published, it's easy to publish sequels, unending sequels, leading to a whole series of books.  Cool and all that, plus doing a sequel is easier on the writer, and the publisher is more likely to make an advance on a known property than take a flier on something new.  So far, so good.
   But, when I am book shopping, the stores don't stock all the books in the series, and even worse, don't stock  the first book of the series. 
  This is a serious turnoff for this reader.  Even if the series has an attractive title, and an intriguing cover illustration and a good blurb, I probably won't buy it if the cover says "Book N is the exciting Yada Yada series". 
  Why?  Simple, authors writing sequels assume the read has read the previous book [s], and save time and work by skipping  (or failing to repeat) essential development material.  In the sequels characters appear, do something, and move on, with never a word about who they are, what side they are on, who they are involved with. 
  Anyhow, you book store operators, you could boost sales by making an effort to keep the first book of the series in stock.