Perhaps both benefit in some ways? (Destiny)

by Durandal, Tuesday, March 15, 2016, 12:36 (3269 days ago) @ Korny

Combining playerbases has some non-obvious benefits to Sony and Microsoft. Niche games will last longer before dropping below the critical player threshold. You don't have to spend millions on risky platform exclusive games, instead you have a much lower cost for platform exclusive gear/maps/content. You also potentially increase the number of games available, and can tempt players who've stuck with other consoles because they won't lose their friends by switching.

It all depends on how much the extra support and validation costs versus the potential savings and cross platform conquest from the above. There should be a bunch of paper pushers somewhere in both companies trying to validate that case.