This is because Rails does not have a strict backwards compatibility policy like many other frameworks. It's done on purpose to stay relevant, aka "Progress over stability".
That would be fine, if it was possible to actually work out what changes you need to make. But Rails will have breaking changes every release that aren't mentioned in the docs. I've spent around 200+ hours over the last year trying to update our app from 5.1 to 5.2. And it's not some kind of megaproject on the scale of Github, its an ordinary app around 10 years old.
Every single Rails update is extremely painful and issues will slip through every unit test and browser automation you can come up with. Stuff that would be trivially catchable with type checking.
Every single Rails update is extremely painful and issues will slip through every unit test and browser automation you can come up with. Stuff that would be trivially catchable with type checking.