You're just not paying attention.
To answer the OP, yes, there are a number of simulators available. But in my experience, they aren't created equally. Most seem to be simulations of standing trackside, watching trains go by (with the exception of ones like Ken posted, above).
Personally, I prefer a simulator that allows you to actually operate a train. As far as steam locomotives go, I haven't seen anything better than this:
This, to me, is a true simulator. Yes, it's based on two narrow gauge 4-4-0s that operate at a famous west-coast theme park. But those locomotives are fully-functioning steam engines, and have to be treated no differently than their main-line counterparts. They are oil fired. And actually, small steam engines such as these are great teaching tools to learn the basics of steam locomotive management. Far easier than jumping into the cab of a Big Boy.
This is a true simulation. Everything is based on physics. You can't add water to the boiler without pressure dropping. If you increase the firing rate, your pressure will increase. Opening the throttle, or even blowing the whistle, will drop the pressure. As the lubrication heats up, the train will run more freely.
You can start the engine cold, in real time, using an air hookup to provide atomization and draft. It will take several hours to reach operating pressure. The "fireman" has to manipulate blower, atomizer, firing rate and water to maintain pressure. The "engineer" has to understand the air brake, and know about "hooking up" to save fuel and spare his fireman. There really isn't any aspect of firing and running a small steam locomotive that hasn't been covered here. You can also set certain functions to be "automatic," so if you just want to concentrate on being the engineer, you can set the engine to fire automatically. You can even quill the whistle.
I own a small library of about 50 catechisms and texts about running steam engines from the 1890s to the 1940s. The manual provided with this simulator is welcome to share shelf space with those authentic volumes.
This simulator was designed and created by someone with an engineering degree, and also someone who has studied steam locomotive mechanics and operation in-depth. If you really want to experience what it's like to be in the cab of a steam locomotive, this is the one for you. All that's missing is the heat.
Full disclosure: Yes, I assisted with the development, including beta testing. I don't benefit from any sales.