> Social network: you only engage on one if your friends/family/coworkers are on the same network.
This one isn't exactly based on fundamental economics given that federated social networks exist. Email has similar network effects and is not centralized.
Some examples:
Social network: you only engage on one if your friends/family/coworkers are on the same network.
Search engine: needs to index "the whole Internet", which is less expensive per user if you have more users
CDN: works best if you have edge nodes everywhere, which is quite capital intensive, which is why you need many customers to distribute it over.
... and so on. We might not like it, but many of these quasi monopolies are based on fundamental economics, not (just) on the greed of the companies.