Why does aim assist exist?

Because this game, among others, puts pc players and console players together in the same lobbies. No, aim assist does not level the playing field, but it creates the illusion of equity. That's not the only reason it exists, but it's one of the big reasons you can never eliminate it from a game that allows players from all platforms to compete against each other.

Now, if you want a history lesson as to why it has always existed in shooters from the console era then we can get into that too. But it's a whole other can of worms and arguably a little harder to justify.

Wanting more revenue, and just plain greed was the back bone of mixed lobbies and platforms. Companies realized that if cross play was implemented, they would have a higher player base, which in turn would generate more profit.   

Personally, I would be ok with people on console having aa, as consoles really do have a disadvantage against pc players with fps and worse set-ups usually. Although, I think the best solution would be to simply not allow crossplay and completely disable aa for console players, but then q times would increase so thats not happening.

But that doesn't justify giving aa to players on pc, who willingly use a controller. If you want to play on a controller, an inherently worse input device, then you likely do it only because of the aa. I still can't see why people on pc with controllers have aa.

And now we're there... pc mnk vs. pc controller. That's a real problem. Although I have to say that if players feel that the transition to controller gives them something that's worth in trade what they have to give up, then that's the way it is. Is there anything stopping a mouse/keyboard player from buying a controller and making the change? Is there any way for the developer to detect the input device and moderate aa accordingly? If there was, wouldn't pc players find a cheat for it inside of a hot minute?

Sorry, but I don't know what the answer is for this one. From what I can see nobody does.

Coming from xbox I am used to controller, there are a few things that are easier on controller imo. I can probably be a case of "I'm used to doing this" but hitting pads underneath the controller is quite fast and on different hands. While you might have a mouse with multiple buttons as well, there are usually more movement for the "keyboard hand" for me.
All that being said, I was never a good apex player and I don't play really play any more, just watching some people that I've become used to.

PC players have significantly reduced aim assist compared to console players (0.4 < 0.6).

Because this game, among others, puts pc players and console players together in the same lobbies.

Um, no.

The way this game handles crossplay is it matches console players with other console players and PC players with other PC players. The only time that a console player would be put against PC players is when said console player is in a party with another PC player.

And conversely, if a pc player is in a party with console players he can end up in a console lobby. So, as I said, this game will under certain circumstances put pc players and console players together in the same lobbies. I'm not saying that I see a lot of them, but even one is one too many.

No aim assist should exist on pc.

Apex and Cod are the only 2 cancerous games where strong aim assist exists on pc. Look at other games like cs2, valorant, they are pc exclusive and have no pro players with controllers. That proves that MnK is just better without any assisting software. My favourite example is Rainbow 6 siege, it has 0 aim assist with cross-play and only 2 pros who use controller (Hmm wonder why apex has so many pros on controller then).

If a game is supposed to be competitive you can't just add aimbot to 1 input device and call it fair. It goes against all standards of competitions.

It would be the same as giving performance drugs to people running marathons in basketball shoes instead of running shoes.

There would ofc be a huge amount of backlash from players who use controllers and would have to learn mnk again, but that isn't anything that would kill apex. Apex has been alive for long enough and already established itself with a solid and loyal player base.

It is a shame that the top-tier of a titanfall game isn't even dominated by mnk and the awesome movement of it isn't used, but instead the highest ranks are filled with people chasing the best possible aim on a controller only because it give aim assist.

Casual pc players wouldn't be affected by the removal of aa because they just don't care enough to play on it, but if you call yourself a competitive player and use a controller then im sorry but you don't even deserve your rank.

Ultimately, removing pc aa would finally turn apex into a serious, competitive game at the cost of the majority of pros / streamers. But in the similar case of Rust the streamers kept streaming and not that many people quit.