I have never tipped the flower delivery person, have never even thought about doing so. The last time flowers were delivered to me the owner of the shop delivered them himself. I doubt he was expecting a tip.
Pizza isn’t delivered as far out of town as we live, but if it was I definitely would tip the delivery person.
[Just saying, delivering flowers is a bit more involved than delivering a cardboard box. We make sure they are fresh, are arranged properly and will even give pointers on how to prolong their vase life. Give the driver a tip, trust me they will appreciate your consideration.