What you are seeing is called the founder's effect. Most of the people that are drawn to a service initially have a subset of shared interests. In the case of steem, it happens to be Crypto because that is what is running everything behind the scenes.

With other websites, the same thing happened, Reddit's early crowd was mostly programmers, and 4chan's early crowd was mainly anime fans.

As websites mature and the demographics get wider, the conversations will open up to cover a wider array of topics and opinions. This will eventually happen over time.