You underestimate how little fucks people give when going on about their day and routine
Even the hard boiled guards and mercenaries don't know the faces of their fellow co-workers all that well, they might know one or two people down the chain, but their job is 99% of being a scarecrow and just standing around, and it gets dreadful when you stand around for hours on end. If an actual assassin were to attack, they would never be able to protect their target, and that's what Hitman games are about.
The barest minimum of a disguise will blend you in with the crowd.
If you wanted to kill someone in this day and age, no matter how wealthy, powerful and prestigious, you could do it, but you being an average citizen, there's so much footprint you've left throughout your life, that you'd be found in an instant and you'd be serving a life sentence. Agent 47 has no background to go after, so he's a ghost in the system.