For one, that there wasn't enough challenging to make backwards incompatible changes.
If it's internal APIs, they need to get on top of deprecating and removing older ones. This is one of the key points of Google's SWE book (at least the first part) and the benefits of a monorepo; if you change an API in a backwards incompatible way, you're also responsible for making sure every consumer is updated accordingly. If you don't, either you're left maintaining the now deprecated API, or you're forcing however much teams to stop what they're doing and put time into a change that you decided needed to happen.
If it's internal APIs, they need to get on top of deprecating and removing older ones. This is one of the key points of Google's SWE book (at least the first part) and the benefits of a monorepo; if you change an API in a backwards incompatible way, you're also responsible for making sure every consumer is updated accordingly. If you don't, either you're left maintaining the now deprecated API, or you're forcing however much teams to stop what they're doing and put time into a change that you decided needed to happen.