The reason: trademark infringement.
AM General, the manufacturer of the military-spec Humvee, has sued Activision Blizzard, the creators of the popular video game franchise "Call of Duty," claiming its trademarks were used without permission. According to Reuters, AM General accused Activision of taking advantage of its goodwill and reputation in the "Humvee" and HMMWV" trademarks when it prominently featured them in "Call of Duty" and other related things such as toys.
Activision claims "Call of Duty" is the world's largest video game console franchise. Since launching in 2003, it's generated more than $15 billion in revenue. No wonder AM General isn't exactly pleased and wants its money. What's interesting is that Activision never received AM General's permission to use the Humvee in the first place. Also, why did it take this long for AM General to do something about this despite a year-long attempt to privately work out a deal? Negotiations fell apart not long ago following a year of trying to come to an agreement. It's now asking for punitive and triple damages from Activision. The civilian version of the Humvee is, of course, the Hummer, which has been out of production for a few years now.
The military-spec Humvee is known worldwide, mainly because it's been in service for more than 30 years. More than 50 other countries also use the Humvee for various purposes. All told, AM General claims it's made more than 278,000 units.