Not sure why the account selector has been introduced? It was just fine when you could just switch between personal and joint account.
I don’t see the point in it because users are only allowed one account using their email and one joint account. So ¯_(ツ)_/¯
It’ll be due to Business Accounts being rolled out also.
To accommodate business account users
Where are you seeing that?
There has always been an account selector for JA holders…
Before this you could just switch to the join account by clicking on the switch account button and you don’t get prompted with the selector shown.
This came out last week iirc.
It needs refining so that if you only have 1 other account it just switches to it instead of asking. Since then it is a given which account you want to view.
Only if you have more than 2 should you see this in my opinion.
I guess we do things differently.
To switch accounts, I’ve always “long pressed” the bottom bar, and then selected the account I want.
I didn’t even know there was another way 
Then I guess it would make more sense to leave it as is (without the selector) until then, because if I read correctly Business accounts might be taking a year or two to be shipped.
They’ve already started shipping to the first 100 companies. 
I do agree, there should be some logic in place – if you have one other account leave it as it was etc.
Account switcher in iOS has always brought up a menu, both pressing the long bar at the bottom and tapping at the top on the Account page
This:
however, has never been implemented even though @Jami has posted a Blog saying that it has been and has never retracted it and ignored every comment on it since.