[brookst]

The monopolies in each segment collapse without the vertically integrated monopoly.

Today you can’t start a ticketing business because Ticketmaster owns so many venues and they won’t use you. You can’t compete in ticket resale because Ticketmaster’s resale gets inventory even before retail tickets are sold.

If these were separate companies there would be no reason, and it would likely be illegal per the breakup ruling, for every venue to use a single ticketing service, or for a ticketing service to use (give a huge advantage to) a single resale service.

The problem isn’t dominance in one segment; that is normal and fine and self-correcting. The problem is leveraging dominance in multiple segments to exclude competition in any of them.