Trademark holders only need to defend their trademark in the product categories they have registered for that trademark. So, obviously a beverage with the word "monster" would be infringing for the drink trademark, they likely should not pursue for the games product category. I looked up their trademark on TESS: https://tmsearch.uspto.gov/bin/showfield?f=doc&state=4805:lk... It is extremely broad, including every conceivable product category but is registered for "Monster Energy"

They might want to plan for the contingency that they might one day release some monster energy related game.