In some cases you can be redirected to the suppliers website for some suppliers. The reason behind it might be because you clicked on the "Punch Out" button from those suppliers.
The Punch Out allows you to access to some suppliers extended catalogue directly on their website, then to export your cart and finalise your order directly in Astore Shop. Want to know more about the Punch Out? Read the following article: Punch Out – Astore Support
If you click on this button you will be redirected to the supplier website: