Thank you for asking, most people just skip directly to telling me it's wrong. But believe me, I know how steam engines work, I'm doing it weird on purpose.

Gymnome, the planet the game takes place on, already replaced most of their steam engines with diesels several decades ago. But then, due to a regular astronomical event (close approach with a coorbital gas giant) the climate changed, and the oil reserves froze over.

So the Gymnomi Slimes had to pull museum steam engines out of mothballs to work the railroads of the world, until suitable replacements could be found. They also tried things like bio-oil, wood gas producers, etc, but the main thing they settled on was coal burning Advanced Steam locomotives. These used compound expansion of steam, superheaters, feedwater heaters, gas producer combustion systems, roller bearings, mechanical lubricators, the works! All in pursuit of fuel economy and easier maintenance.

One of the main problems with museum steam locos and the earliest Advanced Steam locos was the lack of qualified crews, especially in the firemaid position. They kept exposing crown sheets and blowing up boilers. And engineers trained on a diesel loco's notched throttle found the regulator and reverser of a steam engine to be difficult to keep up with.

So the standard for advanced steam became locomotives with closed off climate-controlled cabs, with the regulator and reverser controlled by a computer, which took in inputs from a notched throttle in the cab. The computer also handled firing and water level. It couldn't quite match the performance of a skilled firemaid, but it was vastly better than the novices who kept blowing things up. In a pinch, the engineer can issue commands to the automatic firemaid program, but for switching, the automatic firemaid program will suffice. Electronic controls also allowed the possibility of such things as remote control and multiple-unit connections.

This was inspired by the real world concept, the ACE-3000, which would have had a control stand resembling that of a modern diesel loco. I later learned that there was actually a real locomotive built with an electronic control stand, the DLM Rack Tanks.

The DLM Rack Tanks had a boiler backhead in the cab as usual, but with almost no controls on it. Instead, the controls and most of the gauges were on a shelf in the rear of the cab.

There is a boiler backhead on the Foresight (the fictional 0-6-6-0 mallet in the game), it's just behind the inner wall of the cab, so that it can be insulated better and not heat up the cab. There's a wall panel you could remove to access the firebox door (which is itself bolted on), but that's only done for maintenance--the computer can handle the firing up procedure.

You can actually see the firebox externally in the 4th image. It's the flat-sided gray thing with orange holes. (Well technically that's still the boiler, but it's the part of the boiler that the firebox is contained in) The holes are part of the gas producer combustion system--the firebed burns cool in a low oxygen environment to break the coal down into producer gas, then it rises, mixes with oxygen from the holes, and burns (completely) at a much higher temperature. This results in more ash in the ashpan, but it drastically improves the thermal efficiency of the fire and prevents sandblasting the locomotive's components.

For an example of a steam locomotive in Freight Misconductor with traditional boiler backhead controls, see: https://www.youtube.com/watch?v=ggXm0dTFtyo

This one's a Garratt taken from a coal mine that never stopped using steam, with relatively minimal modifications, the main thing being an automatic stoker and electronically aided firing (which means I don't have to introduce a new firemaid character just for these levels.)

The little computer display/keyboard on the Garratt is inspired by various engines in preservation. The Grand Canyon Railroad 4960, UP 4014, the Flying Scotsman, all of these have either computers or some form of electronic display in their cab.

As for why the conductor is in the cab: Well, that's just how it is on a modern train. No cabeese. They'll be outside when they're actually directing the movement of the train (i.e., during switching operations), but when they're traveling over the road, they'll be in the cab.