BASIC had been aggressively trimmed down to fit into an 8K ROM on the first machines, and there just wasn’t room for much more than crude SAVE and LOAD commands unless we gave up something else. Expanded “disk basic” variants came later, but these were all non-standard.

CP/M and DOS were indeed pretty weak, but this was a time where being first to market with a minimum viable app was everything, and then compatibility with what had already shipped first stalled progress.