One thing you see quite a bit when rummaging around forums are comments like, "OMG that game sucks! Those devs don't know how to make a game." Often these comments are laced with more expletives and leet speek than my example which is understandable since gamers are very passionate and loyal creatures. These comments are somewhat hard (painful) to read as they infer that the developers as a whole don't know what they are doing. Trust me, that's not true. There are plenty of other reasons why MMOs don't end up quite as good as they should...
MMO developers don't try to make bad games - it's in nobody's interest to do so. Since MMOs are massive games with colossal amounts of content and really long development times (typically at least four times as long as a console title), the plan is to recoup the vast majority of the development costs through subscription or micro-transaction fees. A bad MMO is a waste of a hundred million dollars and five years of everyone's time. A bad console game can make money if marketed well - an MMO will not. Believe me, every developer on an MMO is trying to make the best MMO ever.
These days, MMO Development teams are full of people with previous MMO experience. It's rare that an MMO will go into production with stakeholders that have no previous MMO experience - it just doesn't happen. I guarantee that every triple-A MMO released in the last three years had an awesome design document at the beginning of development.
So, how do things go wrong?
SCOPE
Here's how it normally goes. Studio X writes an awesome design for a new game. They approach "the Publisher" with whom they already have a relationship and make a pitch asking for Y million dollars. Publisher gives Studio X a briefcase containing Y million dollars in a dark parking lot and tells them they want a triple-A MMO released by specific date Z. Studio X signs the contract. Everyone is very excited. Hey, we're gonna make a kick-ass MMO, right?
Of course, it's a bit more complicated than that. Especially since, if Studio X has "low-balled" on either Y or Z, the game will suck. "Already?" I hear you ask. Yup, pretty much ... and they haven't even begun preproduction yet.
The studio just signed a contract and got Y million dollars. This has to pay everyone's salaries until the release date, which the studio just promised was on Zeptober the ZZth 20ZZ. That's years away. We can make an MMO by then, right? The studio now knows how many people they can hire and how much they can pay them. Hopefully, this is enough people to make all of the features they just promised.
An MMO has a huge number of moving parts. Scheduling one is really hard. As the game goes into production and gets closer to launch, there is a good chance that the studio's initial estimate for the release date was wrong or that the game design has been revised to be more competitive with the current market leaders (remember five years could have gone by), or that a bunch of guys jumped ship and started their own company, or any number of unforeseen events have occurred.
It becomes clear that there is not enough time for the studio to finish the game that they promised by Zeptober the ZZth 20ZZ. At this point, there are three things the studio can do.
Usually, the studio does a combination of all three. All three steps result in a lower-quality game, especially step three. The harder you cut scope, the suckier your game will be.