Because Haskell isn't used in the same domains as Erlang, and hot patching full Haskell semantics either isn't needed, or the program is likely already using a DSL for the parts needing well defined dynamism, like the Yi editor, and so hot patching the runtime isn't needed.

Why would you need to? GHCi supports dynamic code reloading which most people do during development. During runtime there’s not so much of a use case though for most people.

Hot code reloading isn't used in practice to much extent in Erlang codebases either. It exists, in my experience mostly for Dev or emergency patch but not for normal release upgrades. Dynamics with tagged values and pattern matching def make Erlang the easiest to hot reload.