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"