The reason I have in mind is that Platform requires and uses more constraints than Nebula. Those constraints are the price to pay for sustainability of Platform (they can be API/version numbering, reproducible qualifiers, process to make sure doc is up-to-date accordingly, strict schedule and rules to include new features...). So adding a dependency from Platform to a project which doesn't enforce such constraints may be an issue to maintain the quality of Platform.
Hence why I think such component should be in Platform if we want to use it in Platform.
That said, I'm not sure that such tip of the day would fit best in Platform. Maybe it could be some EPP bundle, like the Marketplace Client; in which case, it's fine ot use Nebula components I believe.
It's a more a design decision between enforcing quality at the price of constraints (Platform) or choosing more agility at the price of lower internal quality requirement (Nebula/EPP).