Popular Science's 2016 article The silliest names scientists have given very serious telescopes... Ranked! says:
Arizona’s MMT Observatory used to house the Multiple Mirror Telescope. In 1998, however, it upgraded to the superiorly-named Massive Monolithic Telescope, which replaced the multiple mirrors of its predecessor with a single 21-foot-wide reflector.
While the article suggests that the name is superior, this isn't a sufficient reason to get rid of the old mirrors and associated positioning instrumentation and buy a new, monolithic mirror.
Question: Why the change, and was it really an "upgrade" in performance?
The Telescope formerly known as Multiple Mirror: