Fifty Years of Open Source Software Supply Chain Security

The xz attack seems to be the first major attack on the open source software supply chain. The event-stream attack was similar but not major, and Heartbleed and Log4j were vulnerabilities, not attacks. But the xz attack was discovered essentially by accident because it made sshd just a bit too slow at startup. Attacks, by their nature, try to remain hidden. What are the chances we would accidentally discover the very first major attack on the open source software supply chain in just a few weeks? Perhaps we were extremely lucky, or perhaps we have missed others.