Unlimited Supreme Court terms were created as a protection against the whims of the executive, as English monarchs had a tendency to fire judges if the positions of the judges differed from their own. However, due in part to the increased life expectancy and polarization of the modern era, life long tenures no longer encourage judicial independence, at least not to a degree that is worth the numerous unintended consequences it has generated. The issue and its causes are multi-faceted, but it can mostly be attributed to a simple fact of modern day, non-political life. The average life expectancy is steadily increasing, meaning that it is not uncommon for justices to serve for approximately 30 years. This increased power, combined with the ever growing power struggle between Democrats and Republicans, has incentivized presidents to nominate someone who will most fervently uphold the values of their party, and senators to manipulate the confirmation process to assure this. Additionally, since the vacancies are left up to chance (when a judge either dies or chooses to retire), some presidents have the opportunity to appoint several justices (Trump appointed 3), while other simply luck out (Carter had 0). Since the justices are likely to strongly reflect the ideology of the president who appointed them (and when, with the electoral college in place, the president may not even represent the majority of the country), this results in an inaccurate representation of the American people and modern values. Evidence of this politicization in action include former Chief Justice Earl Warren choosing to resign under Lyndon B. Johnson in order to avoid being replaced by a Republican president, and Mitch McConnell blocking Obama's 2016 nominee Merrick Garland but then eliminating the filibuster for a Republican nominee and confirming Amy Coney Barrett under the same circumstances for which he blocked Garland. The most commonly proposed solution is a limit of 18 years, meaning that a new justice would be appointed every two years, allotting two nominations to each president. This would give them ample time to learn the job, and still provide the cushion of being relatively unaffected by current political pressures by way of not having to win re-election every few years, while ensuring that the people tasked with making some of the most crucial decisions for the country accurately represent its people. More information on the case for Supreme Court term limits can be found here: https://fixthecourt.com/fix/term-limits/ https://www.americanprogress.org/issues/courts/reports/2020/08/03/488518/need-supreme-court-term-limits/

In either case, we need a system in which the interpretation of the constitution is not predicated on the whims of whoever happened to be in office at the moment of a retirement or death, or whoever is willing to sit and arbitrarily block all options presented. The courts interpreting the constitution should be as far removed from US party politics wherever possible.