^
Because in EA speak, MP is code word for many other things. Such as microtransactions. Or always-online DRM. Or a requirement in order to get certain story outcomes in the SP. Take your pick.
If DA3 comes out with a simple couch or invite-based co-op, with no extra incentives or revenue generation other than it being a cool-ish feature, you can have my shoes. The very shoes on my feet - I will give them to you.
Besides, ME3's shooter/Horde style of MP is neither co-op nor an MMO, so there are tons of variations beside those two things. It doesn't mean that it is ever a good thing. Maybe a neutral thing, where players who don't like it can ignore it... but at the same time, why would they include it unless they thought it would make them more money?
And MP can only make more money if it A) sells more copies of the game or

has some back door way to prevent used game sales, or charge players microtransactions, etc. Given the number of DA fans who decry and protest the very idea of MP, I SERIOUSLY doubt if they include it, that it will generate more sales. So it would seem logic tells us that either they are planning to make more money through the B Reason listed above, or the budget is spent on making a weak or undesired MP component which could have either been used to enhance the SP campaign or to reduce the budget of the game, lowering the threshold point where Bioware needs X units to sell in order to meet profit margin predictions.
So if protesting MP works to keep it out of a game, it results in one of three things: 1) It prevents a generally harmless and non-essential but somewhat fun segment of the game being produced which could bring a small, marginal amount of sales in, 2) It averts the developer putting in tacky design options to separate more players from the money in their wallets, or 3) It lowers the total budget of the game, making it easier for the game to be a success and produce more quality sequels. Conversely, it could also result in more theoretical money for the SP campaign if it is decided that having the MP feature will not result in more sales (which, as I stated earlier, I SERIOUSLY doubt that having "new MP component!!!" on the box of a DA game will cause enough sales to counterbalance the cost it would take to make as well as the number of lost sales to people who protest MP).
Just my two cents.