Because in many cases there might not be innovation, like in cornering the market on a raw material. And monopolies reduce innovation. Remember, Microsoft’s decline is not due to innovation on the desktop or laptop which they block, but because of a totally new platform. We might have a much better desktop/laptop platform today without them, and a thriving market. Who knows? In the long run we are all obsolete is not a good reason to permit monopolies.
You did not need Lehman books in 2010 to know how deep in debt they were in 2008 because their counterparties booked it right.
As has been pointed out, “Widget” could mean anything, including natural resources.
I’d also like to point out that your “historical” solution to the problem of monopolies has absolutely nothing to do with the actual production of widgets, so using it as a solution is merely hoping something will come along which makes widgets obsolete. And in the meantime, nobody else can compete with the widget manufacturer.