As part of a single person household it feels weird that there is a norm that you are allowed to share logins "within your household". Effectively this means people in the same household are paying a lower price than others - so people living in single households are effectively subsidizing that usage by paying more per person.
Each tier has a number of simultaneous streams allowed. If you want multiple people to be able to stream at once you pay more, and if you are streaming one at a time on the same device, you really think each person should have their own account?