There are three questions -
1. Do people spend money to use/buy these types of computer just for "playing games"?
2. Do they take Gaming that much 'Serious' task. I mean is there any hidden benefits in game playing?
3. What makes gaming industry so popular?
Gaming industry is not dependent on the gaming computer/laptop but on the mobile device or tablets for low end games and gaming consoles (VR/AR) for the high end games.
Though I would not say that gaming is beneficial as its harmful impacts are more then its benefits. Some of the benifits are Improvements in basic visual contrast sensitivity, Improved spatial attention in few cases, Improved ability to track moving objects in a field of distractors, Reduced impulsiveness, overcoming dyslexia, Improved ability to engage in multiple tasks simultaneously, Increased mental flexibility, Reversing mental decline that accompanies aging and Improvements in job-related skills.
For me gaming industry is more popular then films and music (dont have the data but I guess spend on the gaming must be more then films and music), simple answer is interactiveness and addictiveness.