I've given this topic a lot of thought, because I've felt similarly on and off. I used to game all the time when I was younger, but in college I largely stopped. I'd still try to play games on vacations, but it began to feel like I was wasting my time; like everyone else was getting ahead with careers or their lives, and there I was, building up characters and hunting for items that wouldn't mean a thing to me in a few weeks.
Part of it is that games have changed, and part of it is that - for those of us who started gaming when we were children - our lives have changed.
Growing up, I was in a suburban area that was borderline rural. I had a limited number of things that I could do. I was also incredibly shy. Games were a way of "getting out" and "meeting people." It sounds silly, but I've read that sentiment from enough people now that I believe there's something to it. It was fulfilling a socialization niche... and this was before true multiplayer games were so prominent. Once you're an adult and you can go where you want and do what you want, that allure of a fictional adventure is a bit less meaningful. I'm no longer choosing between playing in the yard by myself and embarking on a digital adventure; it's a fictional, digital adventure versus heading out to do something else, spend time with friends, or spend time with family (that becomes a lot more meaningful once you've lived on your own, away from your family).
That our lives have changed also plays a large role. School may have felt lengthy, but in hindsight, we had a lot of free time growing up. Schoolwork was engaging to varying levels, but we had hours we could spend immersed in these virtual worlds. Free time really dried up once I started working; I'd still fit a game in here and there on vacations, but then I knew that I had a deadline to finish them. That removes some of the romantic notions behind getting lost in a virtual world. I considered playing games on weekends, but it's difficult to really care about the game world when you're not exposed to it regularly. You forget certain characters or elements of the story. Games involving repetition or grinding are also perceived very differently. Grinding and repetition never felt particularly great or fun when we were younger, but we were still engaged; now it just feels like a chore, and really like a waste of time.
I think that there are also options for games that are much more complex now. I don't remember games keeping track of play time when I was younger (some did, but I never paid attention to the numbers), but it seemed like no game could be long enough. I'd burn through games in one week, even trying to get 100% (or 110%, as some games went). I'd keep playing after because it would be some time before I would be allowed to get a new game, and I'd just be trying to uncover every little secret or glitch. Big-title games now have seemingly become longer. I played Ookami after finishing college, which was an amazing game... and at 100 hours of play time, it was easily my longest game. I don't think other games had broken the 70-hour mark until then. Immediately after Ookami I played Persona 4, which I beat in 120 hours... rushing it, because I was about to begin graduate school. Most recently, I had a relaxed year in which I played Zelda: Breath of the Wild. Even without finishing every single challenge and uncovering every single secret, my total play time was somewhere around 180-190 hours.
Where were games like that when we had all the time in the world? I would have absolutely loved huge games like that! They're still amazing now, but it's a lot more difficult to fit them in. And if you're busy, such huge games may not present enough feelings of making progress to feel satisfying when played in short, infrequent bursts. That games have also become more complex in their mechanics doesn't help: look at the old Nintendo controller, with its D-pad and two buttons, and compare that with the modern game controller. While it's been rare, I'm increasingly coming across games that use every single button on the controllers. Developing that muscle memory for which button does what takes time and reinforcement with practice, again not conducive to playing in short, infrequent bursts. And if you can't even get the button layout down, you're essentially crawling instead of running - and that's far less fun.
The last thing is consideration of the experience effect. My favorite Final Fantasy is Final Fantasy VIII. It's the first one I played. It seems like the first Final Fantasy that people play tends to be their favorite. Why? I'd guess that it's because it's fresh and new, and you will compare everything that you play afterward to it. New and novel things are memorable and exciting. Whether it's a storyline or gameplay mechanic, the more games you play, the more difficult it will be to find something new and novel.
I still consider myself a gamer at heart, even though I'm probably averaging one game a year or less at this point. My wishlist is huge, as is my list of games that I've actually purchased and not yet played. I like to think that they'll be there for me when I retire, but who knows? Maybe I'll be filling my time with something else at that point, too... and no doubt, games will be very different then than they are even now. It's an exciting thought, and somewhat of a sad one too.