Bioware games in general have really never been all that financially successful with the mainstream audience, but the thing with them are that they have a pretty decent sized core fanbase who buys most of the games they do put out pretty consistently, and is thus a pretty safe investment from EA's side.
I'm not sure if the bolded is entirely true. Most of Bioware's recent games have sold millions of copies. They might not have had Skyrim or Call of Duty numbers, but 20 million+ isn't the norm even for most successful games. Holding Skyrim up as the benchmark for success would be like claiming a film isn't successful unless it makes the sort of money that the Star Wars films, Avatar, or Titanic made.
It also all depends on a budget. A game could even sell under a million copies and still be a great success, depending on its development and marketing budget.
I never got the sense that Bioware had a lot of games that were commercial bombs. Maybe SWTOR or Dragon Age 2, but DA:O, DA:I, and all the Mass Effect games seemed to be hits for Bioware. I'm also not even sure that SWTOR or DA2 were bombs. SWTOR is still running strong after transitioning to F2P model and DA2, while less successful than DA:O, might have initially benefited from the DA:O hype preorders.