It's just what ran on the various 8080/Z80 machines that flooded the market in the late 70s. There weren't really any alternatives.
As for the prevalence of its concepts, Gary Kildall borrowed a lot from minicomputer OSes that he was exposed to early in his career. CP/M brought a lot of the capabilities and styles of those $$$ systems to machines that people could use at home. So I think if you want to see where this style of CLI came from and why those things were popular you might look at DEC TOPS-10... or other "real" minicomputer operating systems that hobbyists coveted but could not afford for themselves.
Before standardization around the IBM PC, CP/M was the only way to get that, really. And there were boatloads of these 8080/Z80 systems out there, all sharing some common attributes but not being 100% compatible with each other, so CP/M is what glued them all together until the great wave of the IBM PC overtook them all.
As for the prevalence of its concepts, Gary Kildall borrowed a lot from minicomputer OSes that he was exposed to early in his career. CP/M brought a lot of the capabilities and styles of those $$$ systems to machines that people could use at home. So I think if you want to see where this style of CLI came from and why those things were popular you might look at DEC TOPS-10... or other "real" minicomputer operating systems that hobbyists coveted but could not afford for themselves.
Before standardization around the IBM PC, CP/M was the only way to get that, really. And there were boatloads of these 8080/Z80 systems out there, all sharing some common attributes but not being 100% compatible with each other, so CP/M is what glued them all together until the great wave of the IBM PC overtook them all.