Okay, airline employee here. I want to clear some stuff up.

Everyone likes to shit on the airlines for many reasons, especially lost baggage, and a lot of it is certainly valid. But what a lot people don't understand is the sheer volume of humans it takes to get even one flight out with all the bags and passengers and fuel on it. If literally one person doesn't do their job, say one lazy ramp agent who leaves your bag in the chute instead of bringing it on the plane, then it has a snowball effect. They send the flight out without the bag, and then they come back and see yours and probably a few others that didn't make it on. They're now schedule to go on the next flight. Which might also have lazy rampers or it's simply a quick turn (stressful for everyone) and certain tertiary duties like that slip through the cracks.

It's also possible that some bags don't get put on because of weight and balance. Planes have take off weight limits, so sometimes bags have to be taken off/not put on in the first place. I've seen people taken off planes because of this.

And to your point about airlines making $$$ and not caring about the bags, they actually do care quite a bit, at least the higher ups do. Losing baggage is obviously a terrible look for an airline so there is profit in being reliable about it. Also have you seen checked bag fees? (Which didn't exist before 2008 btw) there's profit in the whole system of checking luggage.

I am not an airline shill, I do not worship any of them, I'm not even defending them. Just hopefully shedding light on some stuff people may not know about.