I fail to see how it would be embarrassing to improve their product. Is it embarrassing for automakers to release a new car with new technology that's better than their last car?
We do not know if next year's car will actually be notably, or even any, better than this year's. The article says they hope so, but obviously nobody knows. Probably there will be fewer of a class of bugs in the new code, but there might also be radically less code implementing needed features. We can only wait and see.
I assure you they’re not embarrassed they didn’t write it in rust from the beginning and they’re not embarrassed to have written the best and most successful browser there is.
We can anyway be certain Google does not need unpaid help defending them.