The backdooring and lack of encryption in software is because the US is still a primary exporter of technology and we want to be able to continue to hack, surveil, message and control those who get US technology. US FedRAMP and other compliance minimums insist on the use of properly configured encryption in private industry to protect government information and cyber sharing programs enable both the sharing of data between private and public sectors for surveillance and for the detection and analysis of foreign cyber attacks. The US government has state of the art encryption (for the most part) and some of the most heavily monitored perimeters.
None of this is enough to stop cyberattacks, which have all of the advantages in their favor.
So while I'm inclined to agree with you that the US should stop mandating backdoors and weak encryption I don't think its a fair characterization to suggest this anything to do with why the US was breached.
China and the US are battling each other in several arenas of influence, as are Russia and the US. In this case the US is trying to stop Russia and China's global and regional power projection and these countries do not accept the US world order and their current place in it.
Conflict is inevitable. It will be interesting to read the history books to see what gets written about the role of the information warfare space and what role it plays in whatever outcome we get.