The biggest advantage by far is the data they collect along the way. Data that can be bucketed to real devs and signals extracted from this can be top tier. All that data + signals + whatever else they cook can be re-added in the training corpus and the models re-trained / version++ on the new set. Rinse and repeat.

(this is also why all the labs, including some chinese ones, are subsidising / metoo-ing coding agents)