What kzt said.
In addition, in reality, there are VERY few ways to reliably knock someone out without killing them. If you hit someone on the back of the head with the butt of your gun, you're as likely to crack their skull and cause a lethal internal bleed, or just annoy them, or genuinely knock them out non-lethally.
Same with drugs. There's a VERY slim line between 'unconscious' and 'dead in 30 seconds from toxic shock'. Just ask an anaesthetist. They get paid a lot of money to knock people out without harming them, and they take a while to properly calculate the flow of drugs according to the patient's weight, medical history, etc etc.
There's a reason cops shoot people with real bullets and not rubber bullets or tear gas or tranq rounds: non-lethal rounds will have no effect a third of the time, kill the target a third of the time, work properly a third of the time. In the first case, the cop might be dead. In the second case, you may as well have used a bullet. In the third case, yay! You win.

But frankly, if you're shooting at someone, chances are lives are at stake, so you may as well use real bullets.
It's in the genre for there to be more reliable ways to knock people out without hurting them, and so it's supported in the game; it's good to see it's not absolute, though.

It's NOT genre for non-lethal options to be more reliable at taking out the target than lethal ones. I remember the WEG Star Wars rules, where shooting stormtroopers with your blaster on stun would take them out more reliably than trying to kill them. I don't remember Luke and Han doing that, so those rules were simply bad.
Me, I'm pondering rules options to make 'non-lethal' more like 'less-lethal'. But the rules as is aren't broken, from what I've seen, it's just my personal preference, not something I think is wrong with the system itself.