In what conceivable way did mass effect out sell Dragon Age? Origins outsold 1 and 2 combined. 3 was the only Mass Effect game that sold well, but was still heavily outsold by Inquisition.
DA was always by far the more popular and better selling franchise.
It depends on where you get your numbers, but it looks like the best selling bioware games are
Mass Effect 3 > Dragon Age Inquisiton > Mass Effect 2 > Mass Effect Andromeda > then the list gets murky, but Baldur's Gate 1 and 2 > KOTOR1 > Dragon Age Origins > Mass Effect 1 > Anthem in there somewhere.
Box Sales are tough because they're never usually explicitly stated and most sites try and extrapolate from a few data points and not an exact science.
Additionally - Box Sales are a very rough metric that aren't fully known (to us). Even if we knew, there are still tons of variables.
- How much was the game purchased for. Games often go on sale after a year or two, so if it's something like DA

that hits a few years later, you're getting $20-30 instead of $60 which is noted by companies.
- How "invested" is the audience for the game (aka, milkable). There was much more DLC in Mass Effect then Dragon Age, presumable because the ME audience was buying it more frequently.
- Cost of Creation - how many people are working on it and for how long? How often can you reuse assets. Mass Effect kept a
lot of the same characters, weapons, armor, locations, enemies, etc which helped to keep costs down. I don't see a lot of DA

being able to be used in DA2, and not much from DA2 moving into DA:I. There was a new Mass Effect hitting every 2.5 years and DLC inbetween the whole time, in essence.
- In the same vein, merchandise. Mass Effect sells, seemingly,
tons of merchandise. Maybe it's anecdotal but I see a ton of N7 shirts, backpacks, jackets etc out in the wild and I've never seen a single piece of discernable Dragon Age merch. This is almost certainly why Marketing liked Mass Effect more - because it was much more marketable.
- Promotional considerations. How many promotional doors did it open? Did video card companies want to bundle keys? Did other channels reach out for promotions (aka limited time events). Did any part of the game go viral?
- Internal considerations. A big factor was likely "did this add users to Origin (the EA launcher)" but a mix of all of the above.
My feeling is by most metrics Mass Effect was the better game. Mass Effect was also easier to market as it was grounded in many more "real world" elements than Dragon Age and while Dragon Age Inquisiton may have outsold Mass Effect 3 - it's super close. But Mass Effect as a series was a much more consistent seller, although it's possible Andromeda and Veilguard did some real damage to any hype a new Mass Effect would generate. My feeling is also Dragon Age 2 really fucked up the DA franchise
badly and is the kind of mistake that should be studied.