It's an engineering reason really, the entire reason why MFTs were so popular when they came out was because people were tired of lugging around their Full-Frame camera's zoom lens, and were sick of missing moments when using a prime lens.

The marketing gimmick for awhile was ultra-zooms which allow for smaller lenses via fixing distortion using DSP, but this degrades the image quality, and so never became a solution for RAW shooters.