We probably don't expect these companies to open source their primary competitive advantages. We expect them to open source things once good_will_value > expected_sales_volume for a given title/piece of software.
The thing is right now Microsoft is getting into the habit of open sourcing things that hit that criteria, and EA is just flatly evaluating that to False every the time. Even when they aren't actively selling a title they own the rights to. The expected value of a title you don't sell is $0 [0], so in effect they're valuing goodwill negatively!
When it's framed that way, it's actually pretty dumb for EA not to be making that calculation. If they do and open source more low sales titles, EA will make more money from better goodwill, and consumers will get more value from older games
[0] This isn't strictly true, because they retain the rights to sell the title in the future, and that option is worth something. But barring very strange circumstances, we expect that if an old title isn't worth the effort to sell today, it likely won't be in the future either. The option is not worth a ton vs. the goodwill of open sourcing it.