“Once Microsoft Edge moves to Manifest V3, ad-blocking extensions won’t have access to the functions needed to properly identify and block ads that occur while browsing websites and watching videos.”
Google wrote Manifest V3, Google sells the ads, and every Chromium browser downstream just inherited the decision. Microsoft had years to fork the extension API and chose not to. The stated reason was always security and performance. The result is that the most effective ad blocker in the world now works in exactly one browser that nobody outside of tech uses.