Shows submitted 5011, but indexed only 706, reason ?

Hi, we have a huge eCommerce store which proper SEO and everything is clean. We get a lot of traffic everyday. All good and well. But if I see google, I was checking today the webmaster tools, I see the total submitted is 5011. But indexed shows 706 only. What could be the reason ? May be, I can check more and fix.

Hi, we have a huge eCommerce store which proper SEO and everything is clean.
We get a lot of traffic everyday. All good and well.

But if I see google, I was checking today the webmaster tools, I see the total submitted is 5011.
But indexed shows 706 only.

What could be the reason ?
May be, I can check more and fix.