I had a book out with rights reverted to me but now still see the book on sale from distributors as new..why?

If it's print as opposed to ebook, the publisher or distributor may still have had some unsold copies. I would expect that your publishing contract allows the publisher to sell those, but not print any new ones.

If you see the book listed as "new" by third-party sellers on Amazon, that just means their copy of the book has never been sold by a retailer to a consumer. It could have been printed years ago and been sitting in a warehouse.

Good answers on print books already, but if it's an ebook, you need to contact the former publisher and demand--politely--that they remove it from all points of sale.

I had this happen just last week. I recognize any business can have some detail fall through the cracks, but I was pretty steamed it was still for sale everywhere even though I now held the rights.

Read your contract, if the book went out of print, all rights go back to the author. If it's considered IN print, the publisher can reprint it.

You will see that for years as long s there are unsold copies form the first printings.