They correctly dismissed it as a curiosity because it was far too inefficient to do anything useful with the amounts of fuel they would have had available. They couldn't have made a more efficient one because they didn't have any idea how to construct reasonably uniform pressure-bearing cylinders.

Real innovation didn't happen until much later on, at British coal mines because 1. there was lots of fuel because it's already at a coal mine, 2. there was a useful task for the work in pumping water out of the mine, and 3. materials technology had advanced enough to make it possible to construct an engine that did a useful amount of work from a manageable amount of fuel.