Vertical integration is definitely one. It's such a big factor it can cause regulators to break up a company. See Google/Chrome as an example from last week.

"SpaceX is vertically integrated" is also not an economic reason for the space ISP market to be winner takes all. Vertical integration doesn't cause breakups. Anticompetitive behavior causes breakups, with or without vertical integration. And vertical integration is not some kind of cheat code to suppress competition. It can be a business advantage but it can also easily be a disadvantage.