If there are rules and laws in place to prevent things like Monopolies (in NA), how is it that a place like Ticketmaster is given the power, and has a complete monopoly over any sale/resale tickets of any event?

Monopolies are illegal because they exploit consumers by fixing prices. Ticketmaster has a large portion of the ticket selling market, but it is not a monopoly. A monopoly has no competitors. Ticketmaster, however, has many competitors, such as Vivid Seats, Prime Sport, Etix, or Ticketfly. Monopolies also exploit consumers and set high prices to increase profits. Ticketmaster sells tickets at reasonable prices. Instead of calling Ticketmaster a monopoly, it can be stated that it is a popular ticket seller.