Of course it's one random night, and of course it doesn't affect people like us, because we watch every week no matter what because it's what we do. But Samurai Jack (and really Super to a lesser extent) is one of those precious few block properties that has grabbed eyeballs well beyond the handful of weebs who still give a damn about dubbed airings on late-night basic cable. We all saw the media blitz its return received on all sorts of big-name entertainment sites. Casual viewers are showing up for this, and they're not used to [as]'s random scheduling bullshit, because self-respecting programming blocks don't do that to popular shows. We know what happened here, but those sorts of viewers tuned in tonight, thought "Wait, where the hell is my show?", and almost certainly didn't stick around to watch anything else. Most of them will be back next week, but given that this final season is so abbreviated in the first place, the absolute last thing you want to do is risk losing any of your audience along the way. You don't need any experience in the television business to puzzle that out.
Like, as soon as someone made the thread about April Fools' falling on a Saturday this year, I remember thinking, "Well whatever they have planned I'm sure they're not retarded enough to do anything with Jack's timeslot." If I didn't know Lazzo was a complete fuck-up beforehand ("Advertising doesn't work!"), this proves it beyond a shadow of a doubt.
(The fact that I'm actually somewhat agreeing with ben's take on things should be enough to tell you that this bugs me.)