Oh, so I think it's too small time for SE to Indexing your pages. More Backlinks, more time and sitemap would helps you!
Also, if you have that many pages, if they arent updated/changed oftern then google will drop them. Happened with a directory of mine. I had 6000+ pages but only 1000 of those pages was fixed solid on google.
I would assume this is more of a search engine optimisation (SEO) question. I believe there is a limit in which google indexes and 30,000 could be it. Email google, you probably wont get a reply, but if you give them a legitimate reason to index the rest of your website, then this may happen. If you have further questions: please feel free to send a PM (Private Message) and i will help you.
first I would like to know ur website which has 5million.. if you didn't uploaded sitemap, do it first..
This is just my opinion : - Increase backlinks - Put more relevan keyword to each page - Try to make each page a little bit different (content,text,banner,etc.) Ideally, google should indexed more than 30k page.Good luck!
can you please show us your site... give the url of site you are talking about.. after seeing it I can give you better idea.. but in general i would agree with what others are saying
First you create a site map and submit your site map in google webmaster tool this is the very helpful you