Sorry for the non-descriptive title, but while I was typing a more descriptive one I realized it was going to be overly long.

My understanding of the USSC appointments is that

• they are for life
• only the US President can appoint a new member
• only the Senate can confirm the appointments

and this comes from the US Constitution.

As a comparison, I have the Italian top Constitutional Court

• appointments are with a term (9 years)
• to maintain balance within the three branches of government, each branch appoints a third of the members (with the President being part of the Executive branch)

This also is detailed in the Italian Constitution.

What has been the political discussion/process that has brought the US to the current rather than other processes?