I know this can come across as very western politically, but I do think it's fair.
Every other country with a checkered past in the 20th century has came full circle and corrected itself.
Japan had been contributing member of the world for 40 years.
Germany had adopted more liberalism, and diversity, and was celebrating its reunification.
South Africa had abandoned apartheid, and despite it's short comings in this area, as their are everywhere, they are working to become better. It was always a nice story to give these countries this event, if you want to call it that, because studies show that host countries and cities don't usually win economically now days.
However, besides what has become a widely recognized issue among football fans. That the Russians are now the biggest hooligans, they are racist, they fight with other fans. Their behavior in France at the Euro's was awful. They subvert UN sanctions with Korea, they invade Crimea and meddle in Ukraine. They systemically oppress homosexuals, minorities, and dissidents. The feudal structure of the state of Chechnya, and the general safety risks presented by that, as well as the terrorism threat that region presents. The horrible job they did with Sochi, be it the cheating or the infrastructure required to host an event of that size and scope.
The list of reasons for Russia to not host a World Cup is very long. To ask why not is to either be contrarian or just to stick your head in the sand.