Readit NewsI once ported Quake 1 to the Rockbox operating system for MP3 players, which enabled it to run on the Apple iPod: https://www.youtube.com/watch?v=r6V-4AZ7pkA
The whole world of software ports basically boils down to "anything is possible, given enough memory, pixels, and time". The actual process of porting anything is sometimes incredibly tedious (e.g. "scour the entire source code for unaligned memory accesses, and manually rewrite all of them"), but also gives a chance to do some very clever things (like, "use the piezo speaker to beep out the address of a fault, because nothing else works on the device after a crash").
What made me do it was 1) the satisfaction I got from seeing my work produce something which, at first glance, shouldn't exist (Quake... on an MP3 player?), all while 2) learning deeply about software close to the bare metal, which is fairly hard to do early in one's career. There's of course also the factor of having lots of free time - I did my port when I was still a student with not very many responsibilities, so I could afford to spend entire evenings and weekends poring through mountains of C code. Nowadays, not so much...
Totally agreed with the reasons for doing ports, huge satisfaction and learning experience; which applies to all of the programming OFC, but here, you also learn from the original codebase (which is in case of Quake phenomenal).