Playground. MS doesn't need them to compete with Sony after shutting down Evolution Studios.
Forza Horizon 3 is their second biggest 1st party title on Xbox One... Considering it's also released on PC the Forza Horizon series has probably made more money than Halo this generation.
LTD: PS4 - 125m, Switch - 110m, XBO - 51m
2020: PS4 - 9m, Switch - 22.5m, XBO - 2.5m, PS5 - 4.5m, XBX - 2.8m