There are 30-something order tables which are associated with orders (including line item, payments, addresses etc. Over time these tables grow very large, which affects not only the size of the tables but also the indexes.
Customers that have run Commerce for a couple of years can easily have millions of orders in the system and tens of millions of line items.
A database design where orders created today "compete" with orders that were made 4 years ago is inefficient by nature.
* The structure will gradually decrease performance as data volume increase.
* The size of the database itself is a cost driver in Azure/DXP.
* It also makes backup handling/exports hard/impossible.
There should be some kind of archival mechanism in Commerce to move historical order data to a more efficient storage, e.g. as serialized JSON (much like the SerializableCart structure.