No, they weren't. It was considered a childish hobby by most people and most of the games were kid games during nintend's reign. Playstation consoles broke sales records that nintendo and the rest dreamt of but couldn't do the vast majority of the time. Playstation home consoles pushed the gaming market into what it is. Third party devs were able to sell record breaking boat loads of games thanks to the success of playstation consoles.
teens/adults becoming gamers was just natural progression, kids in the 80s became teens/young adults in the 90s so developers/publishers naturally made games to cater to their maturing customer base.
That's part of it but as they made more adult focused games, it drew a lot broader range of consumers to gaming which changed the stigma surrounding gaming being a kid's hobby which in turn drew in even more consumers.