A call to $this->logger->info() inside an entity looks harmless. It is one line, it does not change any state, and everybody agrees that logging is useful. Yet from that line on, your domain imports a technical interface, your unit tests need a mock to instantiate the entity, and the layer that is supposed to depend on nothing already depends on something.
Most PHP code treats password hashing as an algorithm choice. You write password_hash($password, PASSWORD_BCRYPT) directly in your authentication code and you move on. It works until the day the recommendation changes, and by then the algorithm you picked is hardcoded in every place that touches a password.
Most PHP projects hardcode their ID generation strategy. Calls to Uuid::uuid4() are scattered across handlers, entities, and tests. When you need to switch to UUID v7 for chronological sorting or ULID for shorter URLs, you end up modifying dozens of files - and hoping you found them all.
Testing code that uses new DateTime('now') or time() is painful. You end up mocking native functions, or accepting fragile tests that fail at midnight.
Direct dependency on a concrete implementation causes the same kind of problems for the logger, the cache, or the ID generator...