[shawnz]

See here where Justin Schuh says the sole motivation is for privacy reasons: https://twitter.com/justinschuh/status/1134092257190064128

I know it is easy to inject JS and that you can do it with the manifest file. But without the old content blocking API you can't dynamically inject different snippets on different pages based on filter lists for example (unless you inject something on every page).

I wouldn't be surprised if in the future, content blocking extensions won't be allowed in the store if they use such broad permissions for example.