It wasn't? Then why did they? As I've repeatedly reminded, sudo is in ports.
I thought credential caching was left out because it was another unnecessary bloated feature creep and doas is supposed to be minimal and more secure. Apparently people couldn't live without it, and it's added in three releases later.
If you followed development, sudo in OpenBSD was maintained by Todd C. Miller, the same person who maintains the sudo.ws version. The version in OpenBSD was years behind and had many features stripped out or disabled. It was a maintenance burden and people wanted the upstream version in ports to get features like plugins, LDAP, etc.
