Besides, at enterprise scale, how do you trust internal teams? It could all be security theater and they aren't delivering on their promises as well.
Some parts of it maybe do. Some others, like multiple different Azure teams, don't even think about anything resembling security, or there wouldn't have been multiple critical and trivially exploitable security vulnerabilities on Azure in the last year only. (If you don't know them, please read up on them. Security is hard, but in those cases nobody even pretended to try!)