You're only thinking about SaaSy things there.
What about on-premises or just open-source software, where you any number of any version of your software may be installed around the universe, and those users need to upgrade to a newer version?
Re:Database schema changes are hard (2017)
by simonw on Saturday March 02, 2019 @11:17AM
(#19289780)
See my comment here about organizations with many engineers and teams: https://news.ycombinator.com/item?id=19289778
No idea why this was downvoted, because this is a key truth.
You need to be able to migrate the production database to the latest version without losing any data.
You need to be able to replace any non-production database with the same schema as production. Ideally, with a (sanitised, subsetted, etc) copy of its data.
You don't need to be able to do anything else.