Why would anyone want to? They don't look any more protective, visibility looks like it would be worse and they don't look any better value than helmets specifically made for cricket.
What lead you to wonder about this?
Exactly the points mentioned by you where I think the opposite. They offer you a better angle of visibility + the grill is attatched to the lid so you don't have any open space between helmet and grill.
Like on this pic you see the chin is protected, the grill is curved downwards, the visibility out of it seems to be pretty good. And I'm not sure about pace bowling argument. As puks are quicker and pack more punch you get them to the helmet as the edges are more dangerous. But at least this could be a good keepers helmet if not for batting.