I suspect this is because a soft rubber will deform more when in contact with the ground under load, so will "squirm" into the irregularities of the surface and tend to hold the tyre in position more positively.
On the other hand, a hard compound, or a tyre inflated very hard, will not deform as much and so will simply move across the surface without interlocking with the irregularities to any great extent.
The average utility cyclist is not going to push the grip abilities of a tyre to the limit anyway as they will be travelling fairly slowly and not cornering fast, but they will certainly notice if their tyres wear out quickly or puncture easily - so it depends on the rider's priority for the tyre's attributes. For most riders, so long as their tyre is round and holds air, they are not going to even notice anything much about it's performance!
Modern tyres are one of the very few areas in cycling where I think there has been substantial advancement in product performance & quality (the other being LED lighting) , as premium quality puncture-resistant, high mileage lifespan, tyres such as the Marathon are light years ahead of the tyres I used to use in the 1980's. I know for some reason M+ are often much maligned on here (I don't use them personally), but the lighter Greenguard version I have found to both roll well and offer decent grip, hardly seem to wear, and I have gone 18 months on them without a single visit from the Fairy. Aside from the fact they are quite heavy, I see no disadvantage to fitting them, I even use them on my drop bar Dawes. which is a fairly sporty frame although not a true racer. I'd sooner be enjoying a trouble-free ride rather than stopped at the roadside fixing flats, so if a few ounces of extra weight in each tyre is the only penalty I have to pay for the extra reliability, to me it's a no-brainer. I haven't gone nuclear with M+ because the ordinary version has proved to be tough enough.