Sometimes people don’t want to take the time to fill out a form with their address, or change their minds when they see there is a small charge for shipping. By getting their email through a double opt-in form, they were educated about the new product through a series of auto-responsder emails, with links back to the free sample page.
It also pre-sells the capture page visitor to the idea that there will be shipping charges to receive the free sample so they don’t feel surprised or tricked like they are on many similar offers.