We want a number, and GDP is a well-known number. As the article notes, there are various replacement proposals, but all get significant push-back from economis

We want a number, and GDP is a well-known number. As the article notes, there are various replacement proposals, but all get significant push-back from economists, and none of them have gained enough critical mass to rival GDP as a thing people quote. So GDP wins by default even though many people are unhappy with it. People are also unhappy with it for pretty different reasons, which doesn't help in consolidating an alternative.