I usually don't feed trolls, which is clearly what you are and we all know it, but I'll bite. These are the significant upgrades
Trevor Siemian
Jay Cutler
Deshone Kizer/Kevin Hogan
Brett Hundley (now that he's a starter)
Brian Hoyer/CJ Beathard
Eli Manning
Blake Bortles
If I had more time I'm sure I could make a case for Rivers (been terrible since last year), McNown, and Rothelisburger (been terrible since last season).
As far as why they'd take the circus, they were ok with Riley Cooper saying he'd fight every ****** at a country concert. They were ok with taken a kicker who beat his wife. Dante Stallworth killed a guy and they were cool with it. None of those people have the talent level of Kaep, but their teams kept them. Those old rich men don't give a fukk about no one being a circus if they can help their team. The reason they wanted Kaep out was to set an example for any other player that got out of line.
		
		
	 
Somewhat misleading, because the situations that you're referring to aren't entirely accurate or 100% the same. Plus there are several players over the years who had questionable on the field and off the field behavioral problems who haven't been picked up either.
There really isn't a one-size-fits-all formula to it.
But just keep in mind that one of the MAJOR differences in your examples is that all of those positions are less prestigious than a NFL QB would be.
QBs for the most part are the face of the franchise. What they do and don't do tends to be under much more scrutiny by the media than a Punter, or WR would.  The only guy off the top of my head who had a similar controversial behavior would be Ben Rothlesburger. But then again, he's headed to the HOF and won two Superbowls, so the Steelers probably looked the other way on it. In otherwords they thought he was worth it.
Vick had the same problem, he was basically blackballed when he came out of a jail. He only got on because he was still EXTREMELY talented and Andy Reid took a chance on him with a rock bottom price. He played well for the Birds, and people overlooked his past, so other teams were willing to take a chance on him once he left.
Kaep isn't Ben or Vick....I don't know what else to tell ya 
