Comment by simonh

Early DOS was designed to be as lightweight as possible so as much memory as possible was available to applications. Including expanded memory bank switching code and 32bit protected mode support on early primitive hardware that didn’t have those features anyway would have left little or nothing for actual applications to run in.

Even when expanded memory was an option, loading a bank switching memory extender to work around the cpu’s Address range limitations left less base memory left for non-EMM aware apps to run in. Many times I remember discussing with users the pros and cons of different memory managers and aporoaches, but most of the time in that era, not using them at all and using bare bones MS-DOS was actually the best choice. Some users would have two boot disks. One without EMM386 to run software that wasn’t expanded/extended memory aware to maximise the memory available to them, and another with EMM386 to run one or two apps that were.