Why upper bound version numbers?

Why would a package developer want to upper bound the version number for packages like base? For example, the clash package requires base >= 4.2 && base <= 4.3 Consequently, it refuses to install with the latest ghc provided with the Haskell Platform (8.0.1). Does this mean that assuming that future versions of the platform will remain backwards compatible with prior versions is unsafe? Thanks, Dominick