That is true, when the cost outweighs the convenience of building on a blockchain, whether that is Ethereum or Steem, building a sovereign blockchain becomes the natural choice.

A lot of blockchains are indirectly gunning for Steem's job. Ethereum is soon getting Akasha, but right now it already has Loom which created DelegateCall as a sample site to display the capability to build Steem on Loom. Then Cosmos is another way to do it effectively, and some social sites are already being built on it.

Ethereum keeps getting abandoned for sovereign blockchain roadmaps and if Steem was expensive for businesses to build on, why not fork?

There is a clear issue here, which is that blockchains and their participants have conflicting interests. Coins/tokens need to have a utility, but at the same time it seems in crypto that coins and tokens can become more expensive than the value they provide to the user, so the user starts fresh.