How is this not anti-competitive behavior? If Microsoft was heavily fined for installing their own browser in their operating system, how is an advertising company like Google using their browser, which has the largest market share, to block competing ads not the same thing?!
Because there are multiple competing products you can switch to, or even multiple additional products (i.e. ublock/adblock) which you can add in Google's own product if you disagree with their stance. It's not anti-competitive just because you don't like it.
Google is leveraging Chrome's dominant market position to (potentially) harm their competitors in an unrelated market.
You were always able to install Firefox or Chrome on Windows, but Microsoft was fined for using their dominant market position (Windows) to push a product in an unrelated market (web browsers).