We were talking about the presentation of "fundamentals" in the courses on Computer Science, right? The fork/exec design is highly non-trivial and so should probably deserve more discussion, with examples of alternative designs and design considerations, than mere "that's how new processes are created, nothing special here, let's move on".
If you want to look at it as ‘fundamentals’, fork only requires the concept of a task, whereas your top-level comment's suggestion also requires (a) secondary storage, (b) organized into files, (c) that can be named.
(That's not why Unix developed with fork, though.)
The (b) and (c) are not really needed: early timesharing systems managed to launch processes straight from the punched card decks IIRC. And without (a), what do you even need the second, identical task for? I guess it could be used parallelize crunching the numbers, but that's it; and probably that should perhaps be done from the system operator layer anyway? Like, "launch 5 copies of program on this deck but mark one specific slot in memory different for them, so they would know their ID".
