Not sure popularity necessarily suggests it's good, but possibly just what people have most heard of or is easiest to setup with. This is going to be even more true now that Claude subscriptions are going to be essentially vendor locked.

Yes. Gemeni's web interface was atrocious even when the model was the best frontier.

And codex still uses phrases and syntax in prose ostensibly for the user as though they forgot people are actively reading this stuff.

Product is unquestionably where Anthropic excels. It is what carried it through periods where its thinking model lagged.