It's not network effects so much as the strength of the two-sided market they've created. Installing an app and registering is a lot of friction. On either side you'll probably bother doing so for no more than one or two services, which in most situations will cover most of whatever market exists.

But in general the answer is either having a disruptive strategy or else a huge amount of money to woo existing market participants. Most of us don't have either. That's the barrier to entry.