IBM had massive style guides put together by committees and based on things they'd done for decades before. Some of what they wanted out of the PC was as a poor

IBM had massive style guides put together by committees and based on things they'd done for decades before. Some of what they wanted out of the PC was as a poor man's mainframe to potentially get more sales of their mainframes. They wanted DOS to look like the solid, stable System/360 and OS/360 they sold (well, leased in most cases), not some weird upstart UNIX clone from IBM's competitors.