Bag of holding vs Howard’s handy haversack

[Desteplo]

Wait.. bag of holding is uncommon and 500lbs capacity

Haversack is rare and is 2 20lbs and 1 80lbs capacity

Why is bag of holding vastly more capacity and more common?

[stoutstien]

Because item rarity isn't a power scale. It like CR but for magic items.

[Joe the Rat]

Because the haversack puts what you need on top - you never have to search.
Unfortunately, this is not reflected in the mechanics. If you could retrieve an item via object interaction, bonus action, or even simple use an object for plucky thieves... or conversely if BoH was more difficult to rummage, then there'd be clear benefits.

The other angle to consider is the bag is a sack, the haversack is a satchel. You can one-hand work that one much easier.

Except that the bag art is a shoulder bag, and for whatever reason they call the haversack a backpack.

Dammit Mearls, go to an REI!