For example, consider that users of component Foo discover that it crashes when it tries to access the internet with BarCorp FireWall 2019 installed. There might be a hotfix released that fixes Foo to not crash.
Since it only affects Foo users that are also BFW users, it might happen that the hotfix happens to break Foo users who have QuuxCorp Internet Optimizer installed instead. The testing might not have caught it since the primary purpose of the testing was to ensure that the issue is fixed for BFW users, with minimal sanity testing that it doesn't break non-BFW users.
So QIO users can mitigate themselves by uninstalling the hotfix. They didn't need it anyway. Eventually another hotfix may be released that supersedes the first one and is tested for both BFW and QIO, and this latter hotfix will eventually be bundled up into a general Foo update.
All this happens independently of another Foo hotfix released after the BFW one, to fix the issue where it crashes when you open a .txt that's actually a .bmp.
The equivalent with Linux packages would be to have .1, .2, .3 package releases, but QIO users can't can't keep the changes in .3 and remove the changes in .2.