All inventions have prerequisites that people don't think about. The steam engine is the first invention people think about if they were time travel, scribble something on a bit of paper and become rich. You'll need several boring things that need to happen for you to make a working steam engine.

You'll need the materials. A lot of strong, cheap steel. Preheated blast furnaces weren't invented until the early 1800's. Thomas Savery had the idea for the steam engine almost a hundred years before the Watt, but Savery's engines kept blowing up because the lack of strong steel.

You'll also need to overcome trade barriers too. You'll also need cheap coal (ironically requiring steam engines to become cost effective) and high quality iron ore (ideally from Sweden). Through out most of history, empires hated trading as it could create vulnerabilities.

There's also the market prerequisites, no one wants your expensive steam engine if a donkey pulling a wheel is cheaper and more reliable.