There's another consideration: portability. Competition among home computer platforms was strong in those days, with new ones coming and going every year; Infoc

There's another consideration: portability. Competition among home computer platforms was strong in those days, with new ones coming and going every year; Infocom could quickly make their entire catalog available for a new machine because all they had to do was port the VM interpreter, then stick it on a disc along with the already-compiled game files. New games would come out simultaneously on every platform they supported; Wikipedia lists those as "the Apple II family, Atari 800, IBM PC compatibles, Amstrad CPC/PCW (one disc worked on both machines), Commodore 64, Commodore Plus/4, Commodore 128,[3] Kaypro CP/M, Texas Instruments TI-99/4A, the Mac, Atari ST, the Commodore Amiga and the Radio Shack TRS-80." (Eventually they expanded the restrictions on the Z-Machine and began creating games too big to fit on the smaller machines, but they were still able to do simultaneous releases on everything with enough room to juggle the larger games.) Also, the VM implemented a domain-specific language, designed with "writing text adventure games" in mind; this was a huge advantage in a time when most games were programmed in assembly language. Both in terms of a faster development cycle, and in terms of building better text-based games by hiring people who were writers first and foremost rather than programmers. (The VM interpreter also implemented virtual memory; while a 128k game file doesn't sound like much, it was pretty huge in an era when typical home computers had 32 or 64k of RAM. Swapfiles didn't exist on anything but huge minicomputers.)