British Airways allow you to register a household account in order to share flight miles. Once you have it you can define your family (up to seven members, sorry Timmy!) and friends and share with them. Except in my case my husband lives abroad, and household accounts presuppose that you live at the same place, and it is not possible to have such an account for just oneself. Were I to include my non-family flatmate in the account I would now presumably be able to share with my husband. As I love to point out to BA, isn’t multi-country families just the customers an airline would like to keep happy? Are people in single-person households bad customers? And would their marketing people really like a database spammed with workaround non-family members?
I suspect that designing, programming and lawyering this kind of routines are not the among the top priority of many companies. The result is a lot of second-rate implementation, a bit like how computer hardware companies often tend to ship good hardware with appallingly bad software.