Personally, I think the people who paid for blockers were ripped off, there's nothing special or difficult in building a content blocker:
1. The majority of the value, the blocking list, it readily available and actively maintained.
2. Performance and integration into iOS is provided by Apple, you simply produce a format that Apple approves.
So what are you paying for? Marketing, packaging, and giving a 3rd party control?
I can think of a few reasons to make a content blocker:
1. Improve privacy for users on the Internet.
2. Decrease cost and speed for people who pay for data, or have bad connections.
3. Challenge revenue streams of large corporations.
4. Fame.
5. Improve strangers lives.