The rewrites tend to involve managerial decisions and not technical (arguably Reddit was one of the few cases where I can point to clear cut technical reasons, the reason being "we wanted to run FreeBSD and threads sucked there"). Sometimes it's internal politics (like JPL's C++ developers giving Lisp as reason for their code segfaulting...).

There's quite a lot of big systems written in Lisp. Unfortunately they rarely ever were opensourced, and we get to have blinders made out of our own limited experiences and common generational knowledge loss in IT.