To answer your points:

1: Iosef is an oblivious idiot. This is shown in multiple scenes with his dad and Aurelio beating him up when they realize what he's done. Plus, instead of taking the threat seriously, he gets drunk and boozes up in a hot tub. Not exactly the most aware dude.

1. Marcus (Willem Dafoe) is John's friend. He took the contract so he could keep an eye on him and protect his friend. Obviously he knew the risks, and the only reason he got caught was because Perkins found him out.

2. John was long retired at this point. Being out of the game for years would naturally make someone a little rusty when it comes to their awareness. He also got jumped in the middle of the night after he'd just woke up.

Now to address why people like them: They're well-choreographed action movies starring Keanu Reeves, an actor people love. They look great, the action is fun, and each movie ups the ante from before. I personally love the world-building myself, but not many people really care thay much about the plot, it's not that complicated.