There is really nothing more about it. Snipers are super popular in EVERY shooter game.
And Widowmaker is the only quote on quote real sniper in Overwatch. She have a scoped rifle, she is there to kill stuff from far ranges. No other hero have that.
Its completely normal that you can see a lot of them. I remember when I was playing Battlefield 4, every server was literally flooded with sniper class, to the point that some server admins started using special plugins that would kill/kick you every time you have picked a sniper when your team already have 4 snipers