It's always easier to cut yourself a path. So why not?
Here, though, there's often a puddle right on the road, but...
... but here there never is.
You save exactly two steps, but still you want to make the path easier.
So why not do the lawn corners rounded from the start? And fewer people cut across and the lawns stay in order.
This post invites community services, landscape designers, environment designers and everyone who knows the answer.
To me it seems this is related to construction simplicity. But then you'd need to break stone blocks into pieces for a rounded radius. And sometimes there's a fence. You'd need to make special rounded fencing for it, and so they just stamped out straight pieces and that's fine.