Firstly, can you list for me the successful MMOs that you have developed? In the probable case you cannot, ill withhold considering your 'expert' opinion and insights into making a MMO.
Futhermore, features can certainly be added later. It is a pity however that players (subscribers) make or break a MMO. It is also a pity that players are not very forgiving. They will not wait a year for you catch up in features. Seeing as the goal for this game is to make a successful and long lasting MMO, i dont think the "add features later" approach is acceptable.
I nor anyone else owes Bioware any patience. If this game were free or did not have a monthly subscription fee, then certainly they would be entitled. However people subscribing to this game are paying for service and content. If Bioware cannot provide it they will stop playing.
As for why one does not simply 'stop playing if you dont like it' . As i have said, many people including myself WANT to like and play the game, however it is difficult to justify doing so if you find fundamental flaws. Futhermore another concern for many players is that they WANT to play a popular and successful MMO. As such there is a concern not just for ones own enjoyment, but perhaps that of others, in so far as it provides more people to play with.