A monopoly is when you do anti-competitive things, not when your product is far and away the most popular.
If anything blame Firefox for dropping the ball so damn hard
Google is an anticompetitive monopoly, and Chrome is an anticompetitive monopoly. This has been established by multiple courts of law. Your armchair claims to the contrary hold no water.
The case ruled that google search was a monopoly for using anti-competitive practices (paying apple to make google the default search) and one of the recommended remedies was selling off chrome. The judge didn't go through with this, likely because in the case they note that people voluntarily really like using chrome, because "edge is the default windows browser that people seem to use only to download chrome".
Check the chair you are in before speaking.
Google is about to break even further away in the LLM race with this move, seeing as they will be getting an absolutely, supremely stunning amount of regular and novel data 24/7. Not everyone uses dedicated LLM interfaces, but more people I know use Google search. As Google === Search for so many.
Nevertheless, it is an business savvy move to make, considering the recent ruling by the judge to not force Google to split apart or break up its business w/r/t to Chrome.