From what I hear single player DLC isn't very profitable anymore in the game industry, which is probably why EA is investing in a loot shooter with microtransactions and not releasing Mass Effect DLC. I would have liked DLC, but it's a sensible decision from a business perspective.
To be fair, though, Mass Effect Andromeda was made by a relatively young team of Mass Effect fans who were given a chance to make a full game after being a support studio for several years. Mismanagement and unattainable goals were allegedly the cause of the game's lack of polish. EA gave BioWare Montreal five years to work on the game (though reportedly they started from scratch 18 months before release when they discovered their ambitious goals couldn't be met) and EA even offered a five months delay if they felt they needed it. I think BioWare takes the full blame on this one.