The challenge with this is that a studio would be alienating fans and making a large investment into an IP and then throwing most of that in the garbage...
Mass Effect isn't enough of a name to carry an untried, unanchored, narrative into the mainstream. Most fans of any work have a superficial relationship to the underlying IP, so most people people who walk into a Batman movie are only gonna want to see Batman, not some "good story" told about unrelated people in Batmans world.
If the story is so solid, and it's so exciting you want to put a hundred million dollars behind it, then why share profits with an unrelated IP owner? Change the 'universe', keep the money. If you're going to pay for an IP, why not use it?
Using established IPs is all about risk management. Paying extra for the joy of increasing the risk is how execs end up not execs ;)
The challenge with this is that a
studio would be alienating fans
Star Was illustrates my point quite nicely: after a couple decades of world building they're already plumbing diminishing returns in one of the worlds largest and most popular IPs only one or two stories removed from their main narrative. I have high hopes for the Han Solo prequel, but Disney isn't putting money behind "alternative" Star Wars narratives until the nostalgia well is tapped, and even then they're going full-court on a trilogy.
Um, Rogue One?
For example, Tomb Raider has to be based on Lara Croft raiding tombs, or it's not Tomb Raider. You have your main character, type of action, and key plot points determined before you start, and viewers will compare them to the games. This is very limiting.
With Mass Effect, you have a rather well realized universe in which you could set a movie that would be easily recognized as Mass Effect, without necessarily being forced to use the main characters from the Game or plot points from the game trilogy. You are given settings, races, ship designs, factions, conflicts, etc. that can be explored from a different angle.
Create a movie that coexists with game plots rather than trying to sum them up or replace them and you'll have more freedom to make a movie that's actually good.
Of course, 95% of everything is crap. Maybe we just haven't seen a good video game movie yet because there haven't yet been enough made to beat the odds. Probably a quarter of the number that have been made were directed by Uwe Boll, and those probably shouldn't be counted as serious attempts at making a good movie anyways.