Did you ever notice the uneven distribution of kids at a typical playground? Let's say there are masses of kids on the climbing equipment. There are fewer on the swings, but it's still a crowd. The slides have just a small handful of children. Only one or two on the merry-go-round. And nobody plays with the spring riders. (The spring rider is the one with the little animal on top of a strong spring. I actually had to look that up. The kid gets on and wobbles forward and back until they fall off or puke. Wheee!) Apparently, most kids would rather stand around and wait for a swing than hop on a spring rider.
If playgrounds were constructed by the people who design your typical MMOG, this would be seen as a design flaw. They would "fix" this problem by forcing kids to play with the less fun stuff before they're allowed access to the more popular toys. The playground would be built like a linear obstacle course. You'd need to grind on the spring riders for 10 minutes before you'd gain access to the merry-go-round. After 15 minutes on that thing you'd be able to have a go at the slides. And so on.
Newbie: Man, this playground is boring.
Old Timer: You just have to stick with it. It's really fun once you get to the climbing stuff.
It's the old World of Warcraft mantra: "The game beings at 80". (Or whatever the level cap is up to these days.)
Let's look at the average MMOG playground and what sorts of amusements they hold:
Solo Play is slow paced and usually has a little bit of story and characters to keep loners engaged.
Group Play is loosely organized play, usually in some sort of instanced location. You throw a random smattering of classes together and stomp around in a ruin. Players tend to skip over the quest text, and they don't waste time gathering a lot of resources because this would hold up the rest of the group.
Raiding is a rigorously organized team-based endeavor that requires a careful balance of classes and a lot of cooperation. Raiding usually demands a solid block of uninterrupted time and some strategic planning beforehand.
PvP is competitive play. (Aside: It's always tough to balance this in a game where power is determined by levels and players spend most of their time fighting AI-controlled monsters. Solo players might want lots and lots of meaningful and varied choices for how they can build and play their character. PvP players will want all of these choices to be perfectly balanced against each other. Good luck with that.)