>>2005974and from another practical perspective, you can bolt down your baskets and you will always have them and they will be there when you get back to where you locked your bike.
with panniers, you either only put them on when you use them, so if you're already out and want to use them for a nearby shop, you have to go home and get them first.
or, if you always keep them with the bike, then you have to always take them with you and babysit them everywhere you go even if you aren't using them or else they'll get stolen. they're also awkward to carry around and many designs won't sit flat on the ground, so they're always tipping over.