My guess is that it is a policy decision to keep the size of the lenses commensurate with the sizes of the cameras.
You can get native lenses in f/0.95 (the Voigtlanders, for example). They are manual focus but invaluable for certain applications.
You can also use adapted lenses - m4/3 is about the most flexible for taking other mount glass. Using focal reducers like the speed boosters can net you very fast glass indeed by using eg a full frame f/1.4 lens on a typical speed booster becomes an f/1 lens on m4/3, and an f/2.8 24-70 zoom becomes something like a 35-100 f/2 equivalent.
But if you've used such a combination you'll know they are bulky, heavy and unwieldy (which can cause problems with mount electronics, rigidity in the lens mount resulting in focus asymmetries and all manner of nasties- I wouldn't want to use my speedbooster off a tripod, really).
So I think that's the reason that the m4/3 manufacturers have concentrated on making physically smaller lenses at the expense of max aperture, rather than slapping an integrated focal reducer on existing fast 35 mm lens designs.
I certainly use m4/3 in the mountains precisely because the whole system- camera, lenses and all- are much smaller and lighter than the APS-C/FF/MF equivalents.
Cheers, Hywel