You really need to have unique TEXT based content on each page to have it indexed. Also if pages are not updated for a very long time, Google will see the page as stale and eventually drop it from the index. Google is looking for current, up to date iinformation. While older sites are trusted, many times, older pages are not and they lose their importance and relevance over time. Google is looking for the most recent, relevant content. That is why blogs do so well in Google.
I can see your point about updated fresh content and why blogs might rank better. But what is a shop supposed to do? Lots of the items in a shop's inventory don't change for several months or new items aren't added in certain categories all the time either. I'm facing a similar problem as the OP with indexed pages. From once more than 2000 are still 600 indexed pages left and this although I do add every month about 30 new products and several older products get discontinued. So there is a certain movement in the inventory/content of the pages and still I can't see any increasing of indexed pages. verdecove
You do it with Press Releases that contain your backlink in it. These are propagated through a variety of means, auto blogs, rss feeds etc. wiscrown
make a sitemap of your site, and submit it to the google. and you should tust the google is the best search engine