It’s a lot of things. The classic argument is that as you get older, you have less free time and therefore less tolerance for things that waste your free time.
“Quantity” is almost universally translated to “Busy Work.” Find all the hidden gizmos, run around in circles a bunch, complete “hard mode” versions of things you’ve already done, and generally just fill time. Thoughtless, mind-numbing padding. Quests for the sake of having literally anything to do.
It makes for a good box quote. “150 hours of gameplay! A never ending quest! You’ll never have to buy another game ever again!”
And when you can only get, say, one game every 3-6 months, that’s awesome! You can wring every last droplet out of that world. Even if it’s kind of lame, it’s better than nothing, right? So if you’re being cheap, or your parents still buy games for you… the bigger, the better.
When quantity isn’t busy work, then it becomes like the Earthworm Jim 2 example I used, or like what Sonic games used to be. I speak from experience when I say that a lot of the hardest work in game development is just getting your game setup. Programming in player physics, control — the fundamentals. Actually building the levels themselves is actually the quickest and easiest part (relatively speaking).
But when you do something like Earthworm Jim 2, each level is almost like a separate game in to itself. What this means is that your “setup” development phase is likely exponentially higher. The team has to shift gears every couple of months as you basically have to re-write your entire game for every level.
Which, needless to say, is costly. Both from the perspective of time and from the perspective of budget. Corners inevitably have to get cut for you to make your deadline, which means everything ends up a little less polished. You might have tons of awesome ideas, but maybe the controls are a little off, maybe animation takes priority over having tight control precision, or maybe you don’t have enough time to fix that bug where the player falls through the world.
Game development resources are finite, meaning you can’t dedicate as much time to fleshing out and tweaking half a dozen different gametypes versus just focusing on one, singular idea.
Mutant Mudds is a fantastic example of this. That game is as simple as humanly possible, but it explores every single possible variation on the concept of jumping and shooting. It may as well be a text book in “doing a lot with a little” game design. It has a laser-focus and was polished to a mirror-sheen.
But bigger numbers are better. You gotta have that box quote, and yours has to be better than theirs.
It’s all about width versus depth. Either you have a lot of things that are shallow, or you have one thing that’s really deep and complex.
You can’t really have both. Not without spending way too much money and 5+ years in development. The real challenge most game designers face is finding the right balance of width and depth. Everything in moderation.
There are definitely people out there who appreciate quality over quantity, though. You just have to look in the right places. And usually, they seem to be older, more experienced gamers who have had their fill of “busy work.”