Reuse Reduce Re-duh

This is not my bag but it's sadly the life and death of many a plastic bag

I was at Wal-Greens tonight and during the checkout/bagging process the lovely and slightly gimp armed cashier who is always so cheerful and happy was putting my sundries into a plastic bag when I saw and purchased a 'green bag'.

I proceeded to remove the items from the Wal-Greens plastic bag and put them into my new reusable bag when she drolly looks up at me and says "I'm just going to throw that plastic bag away". I asked, "You won't use it for the next customer?" She replied, "I'm just going to the bag away." My next sentence was going to be "WTF are you kidding me?" but I held my tongue, took my reusable bag and my plastic bag and left.

How much sense does that make to throw away a just about unused bag in perfectly good condition - especially given the fact that they sell and I bought a REUSABLE bag? People kill me.