The packers are the frequent target to blame on threads like this. But in a large warehouse the packaging "decisions" are made by volumetric software systems. The box is the first item picked then individual items are added to it.
With the opening post it's easy to see what's happened. The length of the tube has determined the size of the box, it's the smallest box long enough to fit the tube. The tube is part of the "item" as it comes from the supplier. Amazon do not ship unprotected product packaging regardless of how solid/protected that product packaging is - even if the tube was large enough to accept a standard Amazon delivery label (which it doesn't look like it could).
A client of mine runs a pick-and-pack, the volumetrics are a PITA to keep on top of. Suppliers are always changing their product packaging, and the software's decisions can be thrown by even minor errors in recorded dimensions.
All this is true, and with warehouses that aren't as fully automated as Amazon, it's often impossible to use the smallest box possible.
1. With hundreds of different products of different sizes, it's impossible to stock a great variety of different size boxes
2. Very fragile items need a good solid box and the right kind of packaging materials, if they are to survive the courier services and, even worse, Royal Mail
3. The job needs to be de-skilled as far as possible, for the simple reason that common sense is extremely uncommon, and this involves setting out rules on the minimum amount of empty space in the box and which materials must be used to fill that space. I had a conversation very recently with an apparently intelligent man about this, he has a masters degree but couldn't see why we pack glass modelling lamps in a box, surrounded by bubble wrap - he thought they they would be fine in a plastic envelope...
Boxes and packing is expensive, and logic says that any efficient business will always use the minimum box size and the minimum packaging, and will also take advantage of small size by sending small items via the large letter service where possible, but for the reasons above, this isn't always possible.