Well, they are not exactly useless. Even discounting for educational games, pointless games like Borderlands / Grand Theft Auto have great value. That value lies in providing entertainment in an interactive way, something that was never possible for most of human existence.

There is something magical about highly interactive games, like say Far Cry. GTA, etc, where the player knows his game, while being the same product, is unique to him/her. Services like Twitch have created whole new ecosystems of micro-economies, where a section of population is replacing movies with watching others playing games. There is great fun in watching an expert gamer playing a game. Part of the experience is in unexpected humor through mistakes, wrong decisions, distractions, etc. Part of the experience is in knowing that none of it is scripted and everything is happening in real time.

As an evolution of the entertainment industry, it's not useless.

There are many negative aspects of gaming as well. If played in excess, at the cost of childhood related activities, like playing with friends outside, etc, it can be detrimental to social development.

But those sorts of problems are there in many areas of life. Anything done in excess is detrimental.