Because it's easy to do. An Intern can slap on pictures on the board of whatever franchise you want to sell, design the few gaming pieces in a freely availble 3D modelling tool and write an email to a production company to produce x amount of said piece. This can be organized by a first year production manager straight out of college on their own, in fact it could be their graduation test if you will.
And the thing is it works - Monopoly is still popular enough, everybody knows the rules ( and probably has a ton of house rules so friends and familes are still able to talk to each other after a game
) and it's a quick way to make some bucks with low effort.
