When the Evolution Collection event was first announced, Apex Legends players immediately started asking questions about the new patch. One of them asked about a leaver penalty.
"If you see this or feel like responding. Is there a reason as to why there is no penalty for leaving public matches?"
Respawn Developer RobotHavGunz did feel like responding.
"So this has been asked a couple of times. It's a mix of technical and UX decisions. Essentially, the system has to be 100% automated; it's not something like content moderation where having some human oversight is practical or reasonable. And, really, it ought to be simple. Because the more complex it gets, the more likely it that something goes wrong. That's why even though I like the idea of something like penalties for frequent leavers, it's also potentially worrisome to add even more complexity into a system. So basically, the system - as it exists - penalizes you if you leave. It doesn't care WHY you left. And that's because 1) it's quite hard (impossible) to truly know why and 2) because if it tried to care why, people would exploit it. So basically, if you leave - whether by accident or because your power went out or your internet went down (has happened to me, and I was penalized for it, as I should have been) - you will get a penalty. Because the impact on your squad is the same regardless of why."
"Given this, from a UX perspective, having a penalty in BR pubs feels overly strict. The idea of leaver penalties is two-fold - one is that you are agreeing not to leave (without consequence) and the second is that your teammates also are agreeing not to leave (without consequence). We only added the penalty to Arena pubs because we saw how impactful a leaver was on the match statistically. We don't see the same impact on BR pubs. Hiding/camping is a viable strategy in BR in a way that it just isn't in Arenas, for example. There are tactical options that are at least possible with a short squad in BR that simply do not exist in Arenas."
"I'm totally in the feelsbadman camp on BR pubs leavers. So I'm not saying this is the "right" decision. I totally see the case for a penalty in BR pubs. But I also see that BR games are already so hard, and so intense - there is no "easy mode" in Apex (especially for not-very-good players like me) - that I think there's something to be said for letting people leave, especially when we have Ranked that's there as the more "serious" alternative. I totally respect the validity of opinions on the other side, though."
Basically the TLDR answer is that public or normal battle royale matches are the closest things to casual matches in the game, and Respawn doesn't want to punish players for leaving.