Hackage recommends using Haskell's PVP[^1], but does not enforce it. That's why many haskell packages are a four-places versions: 3 required and fourth optional (but popular) that represents "other" changes, like documentation.
(no idea but) I feel like changing the first number has a psychological issue, but the 2nd number feels more important than just "minor" sometimes. So may as well let the schema set the mind free?
[^1]: https://pvp.haskell.org/
Why are they requiring two numbers to represent one (semantic) number?