From what I understand, there are currently events which gave you the ability to inspect, and also cancel a request if you want. This allows you to do things like cancel a request if it's trying to download a big video file.

But Google wants to remove the ability to cancel a request through the events, and they want to replace that with declarativeNetRequest[1]. If you look at the link, in the Rules section, it seems to be simple, kinda hardcoded (but configurable) filters.

You can also see there's a limit of only 30,000 rules[2], which is not enough for EasyList[3] (example used in the tracker), which seems to have ~74,000 rules.

This is not targeted to ad blockers specifically. It's a change that makes blocking requests less flexible. For example, uBlock and uMatrix rules can be overridden by more specific rules, something that declarativeNetRequest can't do.

1. https://developers.chrome.com/extensions/declarativeNetReque...

2. https://developers.chrome.com/extensions/declarativeNetReque...

3. https://easylist.to/