Start9 confirmed there are some campatibility issues with template construction using DATUM and btc core together, at least from the research that they scrounged up on my behalf. So, its my guess that Ocean are optimizing the user experience for those start9 / umbrel setups by only allowing knots...then if a user wants to make it work with core its still an option for the more technically savvy that will be running their own server stack. That's my takeaway and my hope for the reasoning.