Writing it in assembly would make it pretty much the opposite of portable (not accounting for emulation), since you are directly giving instructions to a specific hardware and OS.
Not necessarily, unless you’re working on something like an OS you’re not usually directly accessing/working on the hardware. As long as you can connect the asm up to your os/driver abstraction layer and the os to hardware apis work the game should be functional. Not to mention RCT targets the x86 assembler architecture which was one of the most popular at the time
That's no less true than games written in C, or otherwise with few dependencies. Doom is way more portable than RCT precisely because it's written in C instead of assembly.
you’re not usually directly accessing/working on the hardware
I mean, you are. Sure, there's a layer of abstraction when doing tasks that require the intervention of the kernel, but you are still dealing with cpu registers and stuff like that. Merely by writing in assembly you are making your software less portable because you are writing for a specific ISA that only a certain family of processors can read, and talking with the kernel through an API or ABI that is specific to the kernel (standards like Posix mitigate the latter part somewhat, but some systems (windows) aren't Posix compilant).
We created the world of monorail 1. Everything exists to bring more people to monorail 1. What is monorail 1? It is a 4 car monorail that takes the shortest possible path back to the start of the station. We have several other attractions at the park such as: The Pit; Memento Mori; Install CSS, but none of them are the main attraction.