Perhaps better intended for the take a modern invention back in time thread. I suspect it all works together.
The Romans had no need for a steam engine powerful enough to propel a galley, so they had no need for metallurgy advanced enough to build such a boiler. If they needed a large boiler, then there would have been motivations to develop better metallurgy and all of the other technology involved in building a steam ship. Which would have spawned other technologies that could use the advanced metallurgy (queue Connections intro music).
Going back to the “servant crisis” history. Lots of the technology involved in household labor saving devices already existed, but was either not popular or not put to domestic use until getting somebody else to do the work became difficult.