Term limits encourage the development of robust laws, systems and institutions which provide a far more stable basis for running a society than having power structures that rely on the brilliance of an individual or individuals. Without terms limits or the like (and there are countless examples not just in history but currently around the world), individuals in power are motivated mostly to preserve that power and have less incentive to work on improvements that will outlast them.
"institutions" is doing a lot of heavy lifting here. This often means bloated bureaucracy. I'm not against big government in any way or form, but inefficient, bloated bureaucracy with a bunch of mandarins doing the real governing since all the office holders get rotated out after their term limits hit, doesn't seem like a good solution.
With term limits individuals in power are motivated to pass laws that help them find their next job.
There are just too many examples of political leaders who achieved beneficial results initially but as their reign extended into decades, things went sour. Putin, Mugabe, Erdogan, Ferdinand Marcos, Mubarak, Hugo Chavez, Castro and even the likes of Gaddafi are commonly viewed as having improved conditions for the citizens initially but eventually left a legacy of degraded legal systems, weak civil services, rotten institutions in general, weakened or non-existent independent media and busted economies. It just doesn't work in practice which why nearly all countries have switched to term-limits.
These are all examples of executives. I agree that term limits on executives are necessary. https://news.ycombinator.com/item?id=48049876 I think they're harmful for legislators.