The xz attack was not a clown show. It’s a well orchestrated attack, with a lot of clever techniques to slip a payload into something that is supposed to be fully open and readable source code. Somebody recognized a difference between what people think ssh&systemd’s dependency graph looks like, and what it actually was. Fuckery went into disabling some technical defenses (a single dot was snuck into an autoconf file! Try to find it.) and SE went into disabling others. The best malware reversers in the world have been shooting caffeine into their eyeballs for 2 days, trying to make sense of latter-stage payloads.
This attack was damn good. They either got unlucky, or there is a small possibility that our spies out-spied them and dropped the dime. Another angle is that they were running out of time - systemd developers were getting nervous about their own surface area and were working to cut that back. The attacker took the chance on running their play before it was fully bulletproofed, because it was in greater danger of becoming an obsolete exploit.